/DICK.B1/IronPython/Runtime/Operations/StringOps.cs

/* ****************************************************************************

 *

 * Copyright (c) Microsoft Corporation. 

 *

 * This source code is subject to terms and conditions of the Microsoft Public License. A 

 * copy of the license can be found in the License.html file at the root of this distribution. If 

 * you cannot locate the  Microsoft Public License, please send an email to 

 * dlr@microsoft.com. By using this source code in any fashion, you are agreeing to be bound 

 * by the terms of the Microsoft Public License.

 *

 * You must not remove this notice, or any other, from this software.

 *

 *

 * ***************************************************************************/



using System;

using System.Collections;

using System.Collections.Generic;

using System.Diagnostics;

using System.Globalization;

using System.Reflection;

using System.Runtime.InteropServices;

using System.Text;

using IronPython.Runtime.Exceptions;

using IronPython.Runtime.Types;

using Microsoft.Scripting;

using Microsoft.Scripting.Runtime;

using Microsoft.Scripting.Utils;



#if CLR2

using Microsoft.Scripting.Math;

#else

using System.Numerics;

#endif



using SpecialNameAttribute = System.Runtime.CompilerServices.SpecialNameAttribute; 



namespace IronPython.Runtime.Operations {

    /// <summary>

    /// ExtensibleString is the base class that is used for types the user defines

    /// that derive from string.  It carries along with it the string's value and

    /// our converter recognizes it as a string.

    /// </summary>

    public class ExtensibleString : Extensible<string>, ICodeFormattable, IStructuralEquatable

#if CLR2

        , IValueEquality

#endif

    {

        public ExtensibleString() : base(String.Empty) { }

        public ExtensibleString(string self) : base(self) { }



        public override string ToString() {

            return Value;

        }



        #region ICodeFormattable Members



        public virtual string/*!*/ __repr__(CodeContext/*!*/ context) {

            return StringOps.Quote(Value);

        }



        #endregion        



        [return: MaybeNotImplemented]

        public object __eq__(object other) {

            if (other is string || other is ExtensibleString || other is Bytes) {

                return ScriptingRuntimeHelpers.BooleanToObject(EqualsWorker(other));

            }



            return NotImplementedType.Value;

        }



        [return: MaybeNotImplemented]

        public object __ne__(object other) {

            if (other is string || other is ExtensibleString || other is Bytes) {

                return ScriptingRuntimeHelpers.BooleanToObject(!EqualsWorker(other));

            }



            return NotImplementedType.Value;

        }



        #region IValueEquality members

#if CLR2

        int IValueEquality.GetValueHashCode() {

            return GetHashCode();

        }



        bool IValueEquality.ValueEquals(object other) {

            return EqualsWorker(other);

        }

#endif

        #endregion



        #region IStructuralEquatable Members



        int IStructuralEquatable.GetHashCode(IEqualityComparer comparer) {

            if (comparer is PythonContext.PythonEqualityComparer) {

                return GetHashCode();

            }



            return ((IStructuralEquatable)PythonTuple.MakeTuple(Value.ToCharArray())).GetHashCode(comparer);

        }



        bool IStructuralEquatable.Equals(object other, IEqualityComparer comparer) {

            if (comparer is PythonContext.PythonEqualityComparer) {

                return EqualsWorker(other);

            }



            ExtensibleString es = other as ExtensibleString;

            if (es != null) return EqualsWorker(es.Value, comparer);

            string os = other as string;

            if (os != null) return EqualsWorker(os, comparer);

            Bytes tempBytes = other as Bytes;

            if (tempBytes != null) return EqualsWorker(tempBytes.ToString(), comparer);



            return false;

        }



        private bool EqualsWorker(object other) {

            if (other == null) return false;



            ExtensibleString es = other as ExtensibleString;

            if (es != null) return Value == es.Value;

            string os = other as string;

            if (os != null) return Value == os;

            Bytes tempBytes = other as Bytes;

            if (tempBytes != null) return Value == tempBytes.ToString();



            return false;

        }



        private bool EqualsWorker(string/*!*/ other, IEqualityComparer comparer) {

            Debug.Assert(other != null);



            if (Value.Length != other.Length) {

                return false;

            } else if (Value.Length == 0) {

                // 2 empty strings are equal

                return true;

            }



            for (int i = 0; i < Value.Length; i++) {

                if (!comparer.Equals(Value[i], other[i])) {

                    return false;

                }

            }



            return true;

        }



        #endregion



        #region ISequence Members



        public virtual object this[int index] {

            get { return ScriptingRuntimeHelpers.CharToString(Value[index]); }

        }



        public object this[Slice slice] {

            get { return StringOps.GetItem(Value, slice); }

        }



        public object __getslice__(int start, int stop) {

            return StringOps.__getslice__(Value, start, stop);

        }



        #endregion



        #region IPythonContainer Members



        public virtual int __len__() {

            return Value.Length;

        }



        public virtual bool __contains__(object value) {

            if (value is string) return Value.Contains((string)value);

            else if (value is ExtensibleString) return Value.Contains(((ExtensibleString)value).Value);



            throw PythonOps.TypeErrorForBadInstance("expected string, got {0}", value);

        }



        #endregion



    }



    /// <summary>

    /// StringOps is the static class that contains the methods defined on strings, i.e. 'abc'

    /// 

    /// Here we define all of the methods that a Python user would see when doing dir('abc').

    /// If the user is running in a CLS aware context they will also see all of the methods

    /// defined in the CLS System.String type.

    /// </summary>

    public static class StringOps {

        internal const int LowestUnicodeValue = 0x7f;

        private static readonly char[] Whitespace = new char[] { ' ', '\t', '\n', '\r', '\f' };



        internal static object FastNew(CodeContext/*!*/ context, object x) {

            if (x == null) {

                return "None";

            }

            if (x is string) {

                // check ascii

                return CheckAsciiString(context, (string)x);

            }



            // we don't invoke PythonOps.StringRepr here because we want to return the 

            // Extensible<string> directly back if that's what we received from __str__.

            object value = PythonContext.InvokeUnaryOperator(context, UnaryOperators.String, x);

            if (value is string || value is Extensible<string>) {

                return value;

            }



            throw PythonOps.TypeError("expected str, got {0} from __str__", DynamicHelpers.GetPythonType(value).Name);

        }





        internal static string FastNewUnicode(CodeContext context, object value, object encoding, object errors) {

            string strErrors = errors as string;

            if (strErrors == null) {

                throw PythonOps.TypeError("unicode() argument 3 must be string, not {0}", PythonTypeOps.GetName(errors));

            }



            if (value != null) {

                string strValue = value as string;

                if (strValue != null) {

                    return StringOps.RawDecode(context, strValue, encoding, strErrors);

                }



                Extensible<string> es = value as Extensible<string>;

                if (es != null) {

                    return StringOps.RawDecode(context, es.Value, encoding, strErrors);

                }



                Bytes bytes = value as Bytes;

                if (bytes != null) {                    

                    return StringOps.RawDecode(context, bytes.ToString(), encoding, strErrors);

                }



                PythonBuffer buffer = value as PythonBuffer;

                if (buffer != null) {

                    return StringOps.RawDecode(context, buffer.ToString(), encoding, strErrors);

                }                

            }



            throw PythonOps.TypeError("coercing to Unicode: need string or buffer, {0} found", PythonTypeOps.GetName(value));

        }



        internal static object FastNewUnicode(CodeContext context, object value, object encoding) {

            return FastNewUnicode(context, value, encoding, "strict");

        }



        internal static object FastNewUnicode(CodeContext context, object value) {

            if (value == null) {

                return "None";

            } else if (value is string) {

                return value;

            }



            object res;

            OldInstance oi = value as OldInstance;

            if (oi != null &&

                (oi.TryGetBoundCustomMember(context, "__unicode__", out res) || oi.TryGetBoundCustomMember(context, "__str__", out res))) {

                res = context.LanguageContext.Call(context, res);

                if (res is string || res is Extensible<string>) {

                    return res;

                }

                throw PythonOps.TypeError("coercing to Unicode: expected string, got {0}", PythonTypeOps.GetName(value));

            }





            if (PythonTypeOps.TryInvokeUnaryOperator(context, value, "__unicode__", out res) ||

                PythonTypeOps.TryInvokeUnaryOperator(context, value, "__str__", out res)) {

                if (res is string || res is Extensible<string>) {

                    return res;

                }

                throw PythonOps.TypeError("coercing to Unicode: expected string, got {0}", PythonTypeOps.GetName(value));

            }



            return FastNewUnicode(context, value, context.LanguageContext.DefaultEncoding.WebName, "strict");

        }



        private static object CheckAsciiString(CodeContext context, string s) {

            for (int i = 0; i < s.Length; i++) {

                if (s[i] > '\x80')

                    return StringOps.__new__(

                        context,

                        (PythonType)DynamicHelpers.GetPythonTypeFromType(typeof(String)),

                        s,

                        null,

                        "strict"

                        );

            }

            return s;

        }



        #region Python Constructors



        [StaticExtensionMethod]

        public static object __new__(CodeContext/*!*/ context, PythonType cls) {

            if (cls == TypeCache.String) {

                return "";

            } else {

                return cls.CreateInstance(context);

            }

        }



        [StaticExtensionMethod]

        public static object __new__(CodeContext/*!*/ context, PythonType cls, object @object) {

            if (cls == TypeCache.String) {

                return FastNew(context, @object);

            } else {

                return cls.CreateInstance(context, __new__(context, TypeCache.String, @object));

            }

        }



        [StaticExtensionMethod]

        public static object __new__(CodeContext/*!*/ context, PythonType cls, [NotNull]string @object) {

            if (cls == TypeCache.String) {

                return CheckAsciiString(context, @object);

            } else {

                return cls.CreateInstance(context, @object);

            }

        }



        [StaticExtensionMethod]

        public static object __new__(CodeContext/*!*/ context, PythonType cls, [NotNull]ExtensibleString @object) {

            if (cls == TypeCache.String) {

                return FastNew(context, @object);

            } else {

                return cls.CreateInstance(context, __new__(context, TypeCache.String, @object));

            }

        }



        [StaticExtensionMethod]

        public static object __new__(CodeContext/*!*/ context, PythonType cls, char @object) {

            if (cls == TypeCache.String) {

                return CheckAsciiString(context, ScriptingRuntimeHelpers.CharToString(@object));

            } else {

                return cls.CreateInstance(context, __new__(context, TypeCache.String, @object));

            }

        }



        [StaticExtensionMethod]

        public static object __new__(CodeContext/*!*/ context, PythonType cls, [NotNull]BigInteger @object) {

            if (cls == TypeCache.String) {

                return @object.ToString();

            } else {

                return cls.CreateInstance(context, __new__(context, TypeCache.String, @object));

            }

        }



        [StaticExtensionMethod]

        public static object __new__(CodeContext/*!*/ context, PythonType cls, [NotNull]Extensible<BigInteger> @object) {

            if (cls == TypeCache.String) {

                return FastNew(context, @object);

            } else {

                return cls.CreateInstance(context, __new__(context, TypeCache.String, @object));

            }

        }



        [StaticExtensionMethod]

        public static object __new__(CodeContext/*!*/ context, PythonType cls, int @object) {

            if (cls == TypeCache.String) {

                return @object.ToString();

            } else {

                return cls.CreateInstance(context, __new__(context, TypeCache.String, @object));

            }

        }



        [StaticExtensionMethod]

        public static object __new__(CodeContext/*!*/ context, PythonType cls, bool @object) {

            if (cls == TypeCache.String) {

                return @object.ToString();

            } else {

                return cls.CreateInstance(context, __new__(context, TypeCache.String, @object));

            }

        }



        [StaticExtensionMethod]

        public static object __new__(CodeContext/*!*/ context, PythonType cls, double @object) {

            if (cls == TypeCache.String) {

                return DoubleOps.__str__(context, @object);

            } else {

                return cls.CreateInstance(context, __new__(context, TypeCache.String, @object));

            }

        }



        [StaticExtensionMethod]

        public static object __new__(CodeContext/*!*/ context, PythonType cls, Extensible<double> @object) {

            if (cls == TypeCache.String) {

                return FastNew(context, @object);

            } else {

                return cls.CreateInstance(context, __new__(context, TypeCache.String, @object));

            }

        }



        [StaticExtensionMethod]

        public static object __new__(CodeContext/*!*/ context, PythonType cls, float @object) {

            if (cls == TypeCache.String) {

                return SingleOps.__str__(context, @object);

            } else {

                return cls.CreateInstance(context, __new__(context, TypeCache.String, @object));

            }

        }



        [StaticExtensionMethod]

        public static object __new__(CodeContext/*!*/ context, PythonType cls,

            object @string,

            [DefaultParameterValue(null)] string encoding,

            [DefaultParameterValue("strict")] string errors) {



            string str = @string as string;

            if (str == null) throw PythonOps.TypeError("converting to unicode: need string, got {0}", DynamicHelpers.GetPythonType(@string).Name);



            if (cls == TypeCache.String) {

                return decode(context, str, encoding ?? PythonContext.GetContext(context).GetDefaultEncodingName(), errors);

            } else {

                return cls.CreateInstance(context, __new__(context, TypeCache.String, str, encoding, errors));

            }

        }

      

        #endregion



        #region Python __ methods



        public static bool __contains__(string s, string item) {

            return s.Contains(item);

        }



        public static bool __contains__(string s, char item) {

            return s.IndexOf(item) != -1;

        }



        public static string __format__(CodeContext/*!*/ context, string self, string formatSpec) {

            return ObjectOps.__format__(context, self, formatSpec);

        }



        public static int __len__(string s) {

            return s.Length;

        }



        [SpecialName]

        public static string GetItem(string s, int index) {

            return ScriptingRuntimeHelpers.CharToString(s[PythonOps.FixIndex(index, s.Length)]);

        }



        [SpecialName]

        public static string GetItem(string s, object index) {

            return GetItem(s, Converter.ConvertToIndex(index));

        }



        [SpecialName]

        public static string GetItem(string s, Slice slice) {

            if (slice == null) throw PythonOps.TypeError("string indices must be slices or integers");

            int start, stop, step;

            slice.indices(s.Length, out start, out stop, out step);

            if (step == 1) {

                return stop > start ? s.Substring(start, stop - start) : String.Empty;

            } else {

                int index = 0;

                char[] newData;

                if (step > 0) {

                    if (start > stop) return String.Empty;



                    int icnt = (stop - start + step - 1) / step;

                    newData = new char[icnt];

                    for (int i = start; i < stop; i += step) {

                        newData[index++] = s[i];

                    }

                } else {

                    if (start < stop) return String.Empty;



                    int icnt = (stop - start + step + 1) / step;

                    newData = new char[icnt];

                    for (int i = start; i > stop; i += step) {

                        newData[index++] = s[i];

                    }

                }

                return new string(newData);

            }

        }



        public static string __getslice__(string self, int x, int y) {

            Slice.FixSliceArguments(self.Length, ref x, ref y);

            if (x >= y) return String.Empty;



            return self.Substring(x, y - x);

        }



        

        #endregion



        #region Public Python methods



        /// <summary>

        /// Returns a copy of this string converted to uppercase

        /// </summary>

        public static string capitalize(this string self) {

            if (self.Length == 0) return self;

            return Char.ToUpper(self[0], CultureInfo.InvariantCulture) + self.Substring(1).ToLower(CultureInfo.InvariantCulture);

        }



        //  default fillchar (padding char) is a space

        public static string center(this string self, int width) {

            return center(self, width, ' ');

        }



        public static string center(this string self, int width, char fillchar) {

            int spaces = width - self.Length;

            if (spaces <= 0) return self;



            StringBuilder ret = new StringBuilder(width);

            ret.Append(fillchar, spaces / 2);

            ret.Append(self);

            ret.Append(fillchar, (spaces + 1) / 2);

            return ret.ToString();

        }



        public static int count(this string self, string sub) {

            return count(self, sub, 0, self.Length);

        }



        public static int count(this string self, string sub, int start) {

            return count(self, sub, start, self.Length);

        }



        public static int count(this string self, string ssub, int start, int end) {

            if (ssub == null) throw PythonOps.TypeError("expected string for 'sub' argument, got NoneType");



            if (start > self.Length) {

                return 0;

            }



            start = PythonOps.FixSliceIndex(start, self.Length);

            end = PythonOps.FixSliceIndex(end, self.Length);



            if (ssub.Length == 0) {

                return Math.Max((end - start) + 1, 0);

            }



            int count = 0;

            CompareInfo c = CultureInfo.InvariantCulture.CompareInfo;

            while (true) {

                if (end <= start) break;

                int index = c.IndexOf(self, ssub, start, end - start, CompareOptions.Ordinal);

                if (index == -1) break;

                count++;

                start = index + ssub.Length;

            }

            return count;

        }



        public static string decode(CodeContext/*!*/ context, string s) {

            return decode(context, s, Missing.Value, "strict");

        }



        public static string decode(CodeContext/*!*/ context, string s, [Optional]object encoding, [DefaultParameterValue("strict")]string errors) {

            return RawDecode(context, s, encoding, errors);

        }



        public static string encode(CodeContext/*!*/ context, string s, [Optional]object encoding, [DefaultParameterValue("strict")]string errors) {

            return RawEncode(context, s, encoding, errors);

        }



        private static string CastString(object o) {

            string res = o as string;

            if (res != null) {

                return res;

            }



            return ((Extensible<string>)o).Value;

        }



        internal static string AsString(object o) {

            string res = o as string;

            if (res != null) {

                return res;

            }



            Extensible<string> es = o as Extensible<string>;

            if (es != null) {

                return es.Value;

            }



            return null;

        }





        public static bool endswith(this string self, object suffix) {

            TryStringOrTuple(suffix);

            if (suffix is PythonTuple)

                return endswith(self, (PythonTuple)suffix);

            else

                return endswith(self, CastString(suffix));

        }



        public static bool endswith(this string self, object suffix, int start) {

            TryStringOrTuple(suffix);

            if (suffix is PythonTuple)

                return endswith(self, (PythonTuple)suffix, start);

            else

                return endswith(self, CastString(suffix), start);

        }



        public static bool endswith(this string self, object suffix, int start, int end) {

            TryStringOrTuple(suffix);

            if (suffix is PythonTuple)

                return endswith(self, (PythonTuple)suffix, start, end);

            else

                return endswith(self, CastString(suffix), start, end);

        }



        public static string expandtabs(string self) {

            return expandtabs(self, 8);

        }



        public static string expandtabs(this string self, int tabsize) {

            StringBuilder ret = new StringBuilder(self.Length * 2);

            string v = self;

            int col = 0;

            for (int i = 0; i < v.Length; i++) {

                char ch = v[i];

                switch (ch) {

                    case '\n':

                    case '\r': col = 0; ret.Append(ch); break;

                    case '\t':

                        if (tabsize > 0) {

                            int tabs = tabsize - (col % tabsize);

                            int existingSize = ret.Capacity;

                            ret.Capacity = checked(existingSize + tabs);

                            ret.Append(' ', tabs);

                            col = 0;

                        }

                        break;

                    default:

                        col++;

                        ret.Append(ch);

                        break;

                }

            }

            return ret.ToString();

        }



        public static int find(this string self, string sub) {

            if (sub == null) throw PythonOps.TypeError("expected string, got NoneType");

            if (sub.Length == 1) return self.IndexOf(sub[0]);

            

            CompareInfo c = CultureInfo.InvariantCulture.CompareInfo;

            return c.IndexOf(self, sub, CompareOptions.Ordinal);



        }



        public static int find(this string self, string sub, int start) {

            if (sub == null) throw PythonOps.TypeError("expected string, got NoneType");

            if (start > self.Length) return -1;

            start = PythonOps.FixSliceIndex(start, self.Length);



            CompareInfo c = CultureInfo.InvariantCulture.CompareInfo;

            return c.IndexOf(self, sub, start, CompareOptions.Ordinal);

        }



        public static int find(this string self, string sub, int start, int end) {

            if (sub == null) throw PythonOps.TypeError("expected string, got NoneType");

            if (start > self.Length) return -1;

            start = PythonOps.FixSliceIndex(start, self.Length);

            end = PythonOps.FixSliceIndex(end, self.Length);

            if (end < start) return -1;



            CompareInfo c = CultureInfo.InvariantCulture.CompareInfo;

            return c.IndexOf(self, sub, start, end - start, CompareOptions.Ordinal);

        }



        public static int find(this string self, string sub, object start, [DefaultParameterValue(null)]object end) {

            return find(self, sub, CheckIndex(start, 0), CheckIndex(end, self.Length));

        }



        public static int index(this string self, string sub) {

            if (sub == null) throw PythonOps.TypeError("expected string, got NoneType");

            return index(self, sub, 0, self.Length);

        }



        public static int index(this string self, string sub, int start) {

            if (sub == null) throw PythonOps.TypeError("expected string, got NoneType");

            return index(self, sub, start, self.Length);

        }



        public static int index(this string self, string sub, int start, int end) {

            if (sub == null) throw PythonOps.TypeError("expected string, got NoneType");

            int ret = find(self, sub, start, end);

            if (ret == -1) throw PythonOps.ValueError("substring {0} not found in {1}", sub, self);

            return ret;

        }



        public static int index(this string self, string sub, object start, [DefaultParameterValue(null)]object end) {

            return index(self, sub, CheckIndex(start, 0), CheckIndex(end, self.Length));

        }



        public static bool isalnum(this string self) {

            if (self.Length == 0) return false;

            string v = self;

            for (int i = v.Length - 1; i >= 0; i--) {

                if (!Char.IsLetterOrDigit(v, i)) return false;

            }

            return true;

        }



        public static bool isalpha(this string self) {

            if (self.Length == 0) return false;

            string v = self;

            for (int i = v.Length - 1; i >= 0; i--) {

                if (!Char.IsLetter(v, i)) return false;

            }

            return true;

        }



        public static bool isdigit(this string self) {

            if (self.Length == 0) return false;

            string v = self;

            for (int i = v.Length - 1; i >= 0; i--) {

                if (!Char.IsDigit(v, i)) return false;

            }

            return true;

        }



        public static bool isspace(this string self) {

            if (self.Length == 0) return false;

            string v = self;

            for (int i = v.Length - 1; i >= 0; i--) {

                if (!Char.IsWhiteSpace(v, i)) return false;

            }

            return true;

        }



        public static bool isdecimal(this string self) {

            return isnumeric(self);

        }



        public static bool isnumeric(this string self) {

            if (String.IsNullOrEmpty(self)) return false;



            foreach (char c in self) {

                if (!Char.IsDigit(c)) return false;

            }

            return true;

        }



        public static bool islower(this string self) {

            if (self.Length == 0) return false;

            string v = self;

            bool hasLower = false;

            for (int i = v.Length - 1; i >= 0; i--) {

                if (!hasLower && Char.IsLower(v, i)) hasLower = true;

                if (Char.IsUpper(v, i)) return false;

            }

            return hasLower;

        }



        public static bool isupper(this string self) {

            if (self.Length == 0) return false;

            string v = self;

            bool hasUpper = false;

            for (int i = v.Length - 1; i >= 0; i--) {

                if (!hasUpper && Char.IsUpper(v, i)) hasUpper = true;

                if (Char.IsLower(v, i)) return false;

            }

            return hasUpper;

        }



        /// <summary>

        /// return true if self is a titlecased string and there is at least one

        /// character in self; also, uppercase characters may only follow uncased

        /// characters (e.g. whitespace) and lowercase characters only cased ones.

        /// return false otherwise.

        /// </summary>

        public static bool istitle(this string self) {

            if (self == null || self.Length == 0) return false;



            string v = self;

            bool prevCharCased = false, currCharCased = false, containsUpper = false;

            for (int i = 0; i < v.Length; i++) {

                if (Char.IsUpper(v, i) || Char.GetUnicodeCategory(v, i) == UnicodeCategory.TitlecaseLetter) {

                    containsUpper = true;

                    if (prevCharCased)

                        return false;

                    else

                        currCharCased = true;

                } else if (Char.IsLower(v, i))

                    if (!prevCharCased)

                        return false;

                    else

                        currCharCased = true;

                else

                    currCharCased = false;

                prevCharCased = currCharCased;

            }



            //  if we've gone through the whole string and haven't encountered any rule 

            //  violations but also haven't seen an Uppercased char, then this is not a 

            //  title e.g. '\n', all whitespace etc.

            return containsUpper;

        }



        public static bool isunicode(this string self) {

            foreach (char c in self) {

                if (c >= LowestUnicodeValue) return true;

            }

            return false;

        }



        /// <summary>

        /// Return a string which is the concatenation of the strings 

        /// in the sequence seq. The separator between elements is the 

        /// string providing this method

        /// </summary>

        public static string join(this string self, object sequence) {

            IEnumerator seq = PythonOps.GetEnumerator(sequence);

            if (!seq.MoveNext()) return "";



            // check if we have just a sequnce of just one value - if so just

            // return that value.

            object curVal = seq.Current;

            if (!seq.MoveNext()) return Converter.ConvertToString(curVal);



            StringBuilder ret = new StringBuilder();

            AppendJoin(curVal, 0, ret);



            int index = 1;

            do {

                ret.Append(self);



                AppendJoin(seq.Current, index, ret);



                index++;

            } while (seq.MoveNext());



            return ret.ToString();

        }



        public static string join(this string/*!*/ self, [NotNull]List/*!*/ sequence) {

            if (sequence.__len__() == 0) return String.Empty;



            lock (sequence) {

                if (sequence.__len__() == 1) {

                    return Converter.ConvertToString(sequence[0]);

                }



                StringBuilder ret = new StringBuilder();



                AppendJoin(sequence._data[0], 0, ret);

                for (int i = 1; i < sequence._size; i++) {

                    if (!String.IsNullOrEmpty(self)) {

                        ret.Append(self);

                    }

                    AppendJoin(sequence._data[i], i, ret);

                }



                return ret.ToString();

            }

        }



        public static string ljust(this string self, int width) {

            return ljust(self, width, ' ');

        }



        public static string ljust(this string self, int width, char fillchar) {

            if (width < 0) return self;

            int spaces = width - self.Length;

            if (spaces <= 0) return self;



            StringBuilder ret = new StringBuilder(width);

            ret.Append(self);

            ret.Append(fillchar, spaces);

            return ret.ToString();

        }



        public static string lower(this string self) {

            return self.ToLower(CultureInfo.InvariantCulture);

        }



        public static string lstrip(this string self) {

            return self.TrimStart(Whitespace);

        }



        public static string lstrip(this string self, string chars) {

            if (chars == null) return lstrip(self);

            return self.TrimStart(chars.ToCharArray());

        }



        public static PythonTuple partition(this string self, string sep) {

            if (sep == null)

                throw PythonOps.TypeError("expected string, got NoneType");

            if (sep.Length == 0)

                throw PythonOps.ValueError("empty separator");



            object[] obj = new object[3] { "", "", "" };



            if (self.Length != 0) {

                int index = find(self, sep);

                if (index == -1) {

                    obj[0] = self;

                } else {

                    obj[0] = self.Substring(0, index);

                    obj[1] = sep;

                    obj[2] = self.Substring(index + sep.Length, self.Length - index - sep.Length);

                }

            }

            return new PythonTuple(obj);

        }



        private static string StringOrBuffer(object input) {

            string result = (input as string);

            if (result != null) {

                return result;

            }

            PythonBuffer buffer = (input as PythonBuffer);

            if (buffer != null) {

                return buffer.ToString();

            }

            throw PythonOps.TypeError("expected a character buffer object");

        }



        public static string replace(this string self, object old, object new_, [DefaultParameterValue(-1)]int maxsplit) {

            string oldString = StringOrBuffer(old);

            string newString = StringOrBuffer(new_);

            if (oldString.Length == 0) return ReplaceEmpty(self, newString, maxsplit);



            string v = self;

            int replacements = count(v, oldString);

            replacements = (maxsplit < 0 || maxsplit > replacements) ? replacements : maxsplit;

            int newLength = v.Length;

            newLength -= replacements * oldString.Length;

            newLength = checked(newLength + replacements * newString.Length);

            StringBuilder ret = new StringBuilder(newLength);



            int index;

            int start = 0;

            while (maxsplit != 0 && (index = v.IndexOf(oldString, start)) != -1) {

                ret.Append(v, start, index - start);

                ret.Append(newString);

                start = index + oldString.Length;

                maxsplit--;

            }

            ret.Append(v.Substring(start));



            return ret.ToString();

        }



        public static int rfind(this string self, string sub) {

            if (sub == null) throw PythonOps.TypeError("expected string, got NoneType");

            return rfind(self, sub, 0, self.Length);

        }



        public static int rfind(this string self, string sub, int start) {

            if (sub == null) throw PythonOps.TypeError("expected string, got NoneType");

            if (start > self.Length) return -1;

            return rfind(self, sub, start, self.Length);

        }



        public static int rfind(this string self, string sub, int start, int end) {

            if (sub == null) throw PythonOps.TypeError("expected string, got NoneType");

            if (start > self.Length) return -1;



            start = PythonOps.FixSliceIndex(start, self.Length);

            end = PythonOps.FixSliceIndex(end, self.Length);



            if (start > end) return -1;     // can't possibly match anything, not even an empty string

            if (sub.Length == 0) return end;    // match at the end

            if (end == 0) return -1;    // can't possibly find anything



            CompareInfo c = CultureInfo.InvariantCulture.CompareInfo;

            return c.LastIndexOf(self, sub, end - 1, end - start, CompareOptions.Ordinal);

        }



        public static int rfind(this string self, string sub, object start, [DefaultParameterValue(null)]object end) {

            return rfind(self, sub, CheckIndex(start, 0), CheckIndex(end, self.Length));

        }



        public static int rindex(this string self, string sub) {

            return rindex(self, sub, 0, self.Length);

        }



        public static int rindex(this string self, string sub, int start) {

            return rindex(self, sub, start, self.Length);

        }



        public static int rindex(this string self, string sub, int start, int end) {

            int ret = rfind(self, sub, start, end);

            if (ret == -1) throw PythonOps.ValueError("substring {0} not found in {1}", sub, self);

            return ret;

        }



        public static int rindex(this string self, string sub, object start, [DefaultParameterValue(null)]object end) {

            return rindex(self, sub, CheckIndex(start, 0), CheckIndex(end, self.Length));

        }



        public static string rjust(this string self, int width) {

            return rjust(self, width, ' ');

        }



        public static string rjust(this string self, int width, char fillchar) {

            int spaces = width - self.Length;

            if (spaces <= 0) return self;



            StringBuilder ret = new StringBuilder(width);

            ret.Append(fillchar, spaces);

            ret.Append(self);

            return ret.ToString();

        }



        public static PythonTuple rpartition(this string self, string sep) {

            if (sep == null)

                throw PythonOps.TypeError("expected string, got NoneType");

            if (sep.Length == 0)

                throw PythonOps.ValueError("empty separator");



            object[] obj = new object[3] { "", "", "" };

            if (self.Length != 0) {

                int index = rfind(self, sep);

                if (index == -1) {

                    obj[2] = self;

                } else {

                    obj[0] = self.Substring(0, index);

                    obj[1] = sep;

                    obj[2] = self.Substring(index + sep.Length, self.Length - index - sep.Length);

                }

            }

            return new PythonTuple(obj);

        }



        //  when no maxsplit arg is given then just use split

        public static List rsplit(this string self) {

            return SplitInternal(self, (char[])null, -1);

        }



        public static List rsplit(this string self, string sep) {

            return rsplit(self, sep, -1);

        }



        public static List rsplit(this string self, string sep, int maxsplit) {

            //  rsplit works like split but needs to split from the right;

            //  reverse the original string (and the sep), split, reverse 

            //  the split list and finally reverse each element of the list

            string reversed = Reverse(self);

            if (sep != null) sep = Reverse(sep);

            List temp = null, ret = null;

            temp = split(reversed, sep, maxsplit);

            temp.reverse();

            int resultlen = temp.__len__();

            if (resultlen != 0) {

                ret = new List(resultlen);

                foreach (string s in temp)

                    ret.AddNoLock(Reverse(s));

            } else {

                ret = temp;

            }

            return ret;

        }



        public static string rstrip(this string self) {

            return self.TrimEnd(Whitespace);

        }



        public static string rstrip(this string self, string chars) {

            if (chars == null) return rstrip(self);

            return self.TrimEnd(chars.ToCharArray());

        }



        public static List split(this string self) {

            return SplitInternal(self, (char[])null, -1);

        }



        public static List split(this string self, string sep) {

            return split(self, sep, -1);

        }



        public static List split(this string self, string sep, int maxsplit) {

            if (sep == null) {

                if (maxsplit == 0) {

                    // Corner case for CPython compatibility

                    List result = PythonOps.MakeEmptyList(1);

                    result.AddNoLock(self.TrimStart());

                    return result;

                        

                } else {

                    return SplitInternal(self, (char[])null, maxsplit);

                }

            }



            if (sep.Length == 0) {

                throw PythonOps.ValueError("empty separator");

            } else if (sep.Length == 1) {

                return SplitInternal(self, new char[] { sep[0] }, maxsplit);

            } else {

                return SplitInternal(self, sep, maxsplit);

            }

        }



        public static List splitlines(this string self) {

            return splitlines(self, false);

        }



        public static List splitlines(this string self, bool keepends) {

            List ret = new List();

            int i, linestart;

            for (i = 0, linestart = 0; i < self.Length; i++) {

                if (self[i] == '\n' || self[i] == '\r' || self[i] == '\x2028') {

                    //  special case of "\r\n" as end of line marker

                    if (i < self.Length - 1 && self[i] == '\r' && self[i + 1] == '\n') {

                        if (keepends)

                            ret.AddNoLock(self.Substring(linestart, i - linestart + 2));

                        else

                            ret.AddNoLock(self.Substring(linestart, i - linestart));

                        linestart = i + 2;

                        i++;

                    } else { //'\r', '\n', or unicode new line as end of line marker

                        if (keepends)

                            ret.AddNoLock(self.Substring(linestart, i - linestart + 1));

                        else

                            ret.AddNoLock(self.Substring(linestart, i - linestart));

                        linestart = i + 1;

                    }

                }

            }

            //  the last line needs to be accounted for if it is not empty

            if (i - linestart != 0)

                ret.AddNoLock(self.Substring(linestart, i - linestart));

            return ret;

        }





        public static bool startswith(this string self, object prefix) {

            TryStringOrTuple(prefix);

            if (prefix is PythonTuple)

                return startswith(self, (PythonTuple)prefix);

            else

                return startswith(self, CastString(prefix));



        }



        public static bool startswith(this string self, object prefix, int start) {

            TryStringOrTuple(prefix);

            if (prefix is PythonTuple)

                return startswith(self, (PythonTuple)prefix, start);

            else

                return startswith(self, CastString(prefix), start);

        }



        public static bool startswith(this string self, object prefix, int start, int end) {

            TryStringOrTuple(prefix);

            if (prefix is PythonTuple)

                return startswith(self, (PythonTuple)prefix, start, end);

            else

                return startswith(self, CastString(prefix), start, end);

        }



        public static string strip(this string self) {

            return self.Trim();

        }



        public static string strip(this string self, string chars) {

            if (chars == null) return strip(self);

            return self.Trim(chars.ToCharArray());

        }



        public static string swapcase(this string self) {

            StringBuilder ret = new StringBuilder(self);

            for (int i = 0; i < ret.Length; i++) {

                char ch = ret[i];

                if (Char.IsUpper(ch)) ret[i] = Char.ToLower(ch, CultureInfo.InvariantCulture);

                else if (Char.IsLower(ch)) ret[i] = Char.ToUpper(ch, CultureInfo.InvariantCulture);

            }

            return ret.ToString();

        }



        public static string title(this string self) {

            if (self == null || self.Length == 0) return self;



            char[] retchars = self.ToCharArray();

            bool prevCharCased = false;

            bool currCharCased = false;

            int i = 0;

            do {

                if (Char.IsUpper(retchars[i]) || Char.IsLower(retchars[i])) {

                    if (!prevCharCased)

                        retchars[i] = Char.ToUpper(retchars[i], CultureInfo.InvariantCulture);

                    else

                        retchars[i] = Char.ToLower(retchars[i], CultureInfo.InvariantCulture);

                    currCharCased = true;

                } else {

                    currCharCased = false;

                }

                i++;

                prevCharCased = currCharCased;

            }

            while (i < retchars.Length);

            return new string(retchars);

        }



        //translate on a unicode string differs from that on an ascii

        //for unicode, the table argument is actually a dictionary with

        //character ordinals as keys and the replacement strings as values

        public static string translate(this string self, [NotNull]PythonDictionary table) {

            if (table == null || self.Length == 0) {

                return self;

            }



            StringBuilder ret = new StringBuilder();

            for (int i = 0, idx = 0; i < self.Length; i++) {

                idx = (int)self[i];

                if (table.__contains__(idx))

                    ret.Append((string)table[idx]);

                else

                    ret.Append(self[i]);

            }

            return ret.ToString();

        }



        public static string translate(this string self, string table) {

            return translate(self, table, (string)null);

        }



        public static string translate(this string self, string table, string deletechars) {

            if (table != null && table.Length != 256) {

                throw PythonOps.ValueError("translation table must be 256 characters long");

            } else if (self.Length == 0) {

                return self;

            }



            // List<char> is about 2/3rds as expensive as StringBuilder appending individual 

            // char's so we use that instead of a StringBuilder

            List<char> res = new List<char>();

            for (int i = 0; i < self.Length; i++) {

                if (deletechars == null || !deletechars.Contains(Char.ToString(self[i]))) {

                    if (table != null) {

                        int idx = (int)self[i];

                        if (idx >= 0 && idx < 256) {

                            res.Add(table[idx]);

                        }

                    } else {

                        res.Add(self[i]);

                    }

                }

            }

            return new String(res.ToArray());

        }



        public static string upper(this string self) {

            return self.ToUpper(CultureInfo.InvariantCulture);

        }



        public static string zfill(this string self, int width) {

            int spaces = width - self.Length;

            if (spaces <= 0) return self;



            StringBuilder ret = new StringBuilder(width);

            if (self.Length > 0 && IsSign(self[0])) {

                ret.Append(self[0]);

                ret.Append('0', spaces);

                ret.Append(self.Substring(1));

            } else {

                ret.Append('0', spaces);

                ret.Append(self);

            }

            return ret.ToString();

        }



        /// <summary>

        /// Replaces each replacement field in the string with the provided arguments.

        /// 

        /// replacement_field =  "{" field_name ["!" conversion] [":" format_spec] "}"

        /// field_name        =  (identifier | integer) ("." identifier | "[" element_index "]")*

        /// 

        /// format_spec: [[fill]align][sign][#][0][width][.precision][type]

        /// 

        /// Conversion can be 'r' for repr or 's' for string.

        /// </summary>

        public static string/*!*/ format(CodeContext/*!*/ context, string format_string, [NotNull]params object[] args) {

            return NewStringFormatter.FormatString(

                PythonContext.GetContext(context),

                format_string,

                PythonTuple.MakeTuple(args),

                new PythonDictionary()

            );

        }



        /// <summary>

        /// Replaces each replacement field in the string with the provided arguments.

        /// 

        /// replacement_field =  "{" field_name ["!" conversion] [":" format_spec] "}"

        /// field_name        =  (identifier | integer) ("." identifier | "[" element_index "]")*

        /// 

        /// format_spec: [[fill]align][sign][#][0][width][.precision][type]

        /// 

        /// Conversion can be 'r' for repr or 's' for string.

        /// </summary>

        public static string/*!*/ format(CodeContext/*!*/ context, string format_string, [ParamDictionary]IDictionary<object, object> kwargs, params object[] args) {

            return NewStringFormatter.FormatString(

                PythonContext.GetContext(context),

                format_string,

                PythonTuple.MakeTuple(args),

                kwargs

            );

        }



        public static IEnumerable<PythonTuple>/*!*/ _formatter_parser(this string/*!*/ self) {

            return NewStringFormatter.GetFormatInfo(self);

        }



        public static PythonTuple/*!*/ _formatter_field_name_split(this string/*!*/ self) {

            return NewStringFormatter.GetFieldNameInfo(self);

        }



        #endregion



        #region operators

        [SpecialName]

        public static string Add([NotNull]string self, [NotNull]string other) {

            return self + other;

        }



        [SpecialName]

        public static string Add([NotNull]string self, char other) {

            return self + other;

        }



        [SpecialName]

        public static string Add(char self, [NotNull]string other) {

            return self + other;

        }



        [SpecialName]

        public static string Mod(CodeContext/*!*/ context, string self, object other) {

            return new StringFormatter(context, self, other).Format();

        }



        [SpecialName]

        [return: MaybeNotImplemented]

        public static object Mod(CodeContext/*!*/ context, object other, string self) {

            string str = other as string;

            if (str != null) {

                return new StringFormatter(context, str, self).Format();

            }



            Extensible<string> es = other as Extensible<string>;

            if (es != null) {

                return new StringFormatter(context, es.Value, self).Format();

            }



            return NotImplementedType.Value;

        }



        [SpecialName]

        public static string Multiply(string s, int count) {

            if (count <= 0) return String.Empty;

            if (count == 1) return s;



            long size = (long)s.Length * (long)count;

            if (size > Int32.MaxValue) throw PythonOps.OverflowError("repeated string is too long");



            int sz = s.Length;

            if (sz == 1) return new string(s[0], count);



            StringBuilder ret = new StringBuilder(sz * count);

            ret.Insert(0, s, count);

            // the above code is MUCH faster than the simple loop

            //for (int i=0; i < count; i++) ret.Append(s);

            return ret.ToString();

        }



        [SpecialName]

        public static string Multiply(int other, string self) {

            return Multiply(self, other);

        }



        [SpecialName]

        public static object Multiply(string self, [NotNull]Index count) {

            return PythonOps.MultiplySequence<string>(Multiply, self, count, true);

        }



        [SpecialName]

        public static object Multiply([NotNull]Index count, string self) {

            return PythonOps.MultiplySequence<string>(Multiply, self, count, false);

        }



        [SpecialName]

        public static object Multiply(string self, object count) {

            int index;

            if (Converter.TryConvertToIndex(count, out index)) {

                return Multiply(self, index);

            }



            throw PythonOps.TypeErrorForUnIndexableObject(count);

        }



        [SpecialName]

        public static object Multiply(object count, string self) {

            int index;

            if (Converter.TryConvertToIndex(count, out index)) {

                return Multiply(index, self);

            }



            throw PythonOps.TypeErrorForUnIndexableObject(count);

        }



        [SpecialName]

        public static bool GreaterThan(string x, string y) {

            return string.CompareOrdinal(x, y) > 0;

        }

        [SpecialName]

        public static bool LessThan(string x, string y) {

            return string.CompareOrdinal(x, y) < 0;

        }

        [SpecialName]

        public static bool LessThanOrEqual(string x, string y) {

            return string.CompareOrdinal(x, y) <= 0;

        }

        [SpecialName]

        public static bool GreaterThanOrEqual(string x, string y) {

            return string.CompareOrdinal(x, y) >= 0;

        }

        [SpecialName]

        public static bool Equals(string x, string y) {

            return string.Equals(x, y);

        }

        [SpecialName]

        public static bool NotEquals(string x, string y) {

            return !string.Equals(x, y);

        }



        #endregion



        [SpecialName, ImplicitConversionMethod]

        public static string ConvertFromChar(char c) {

            return ScriptingRuntimeHelpers.CharToString(c);

        }

        

        [SpecialName, ExplicitConversionMethod]

        public static char ConvertToChar(string s) {

            if (s.Length == 1) return s[0];

            throw PythonOps.TypeErrorForTypeMismatch("char", s);

        }



        [SpecialName, ImplicitConversionMethod]

        public static IEnumerable ConvertToIEnumerable(string s) {

            // make an enumerator that produces strings instead of chars

            return new PythonStringEnumerable(s);

        }



        internal static int Compare(string self, string obj) {

            int ret = string.CompareOrdinal(self, obj);

            return ret == 0 ? 0 : (ret < 0 ? -1 : +1);

        }



        public static object __getnewargs__(CodeContext/*!*/ context, string self) {

            if (!Object.ReferenceEquals(self, null)) {

                // Cast self to object to avoid exception caused by trying to access SystemState on DefaultContext

                return PythonTuple.MakeTuple(StringOps.__new__(context, TypeCache.String, (object)self));

            }

            throw PythonOps.TypeErrorForBadInstance("__getnewargs__ requires a 'str' object but received a '{0}'", self);

        }



        public static string __str__(string self) {

            return self;

        }



        public static Extensible<string> __str__(ExtensibleString self) {

            return self;

        }



        #region Internal implementation details



        internal static string Quote(string s) {



            bool isUnicode = false;

            StringBuilder b = new StringBuilder(s.Length + 5);

            char quote = '\'';

            if (s.IndexOf('\'') != -1 && s.IndexOf('\"') == -1) {

                quote = '\"';

            }

            b.Append(quote);

            b.Append(ReprEncode(s, quote, ref isUnicode));

            b.Append(quote);

            if (isUnicode) return "u" + b.ToString();

            return b.ToString();

        }



        internal static string ReprEncode(string s, ref bool isUnicode) {

            return ReprEncode(s, (char)0, ref isUnicode);

        }



        internal static bool TryGetEncoding(string name, out Encoding encoding) {

#if SILVERLIGHT // EncodingInfo

            switch (NormalizeEncodingName(name)) {

                case "us_ascii":

                case "ascii": encoding = PythonAsciiEncoding.Instance; return true;

                case "utf_8": encoding = (Encoding)new EncodingWrapper(Encoding.UTF8, new byte[0]).Clone(); return true;

                case "utf_16_le": encoding = (Encoding)new EncodingWrapper(Encoding.Unicode, new byte[0]).Clone(); return true;

                case "utf_16_be": encoding = (Encoding)new EncodingWrapper(Encoding.BigEndianUnicode, new byte[0]).Clone(); return true;

                case "utf_8_sig": encoding = Encoding.UTF8; return true;

            }

#else

            name = NormalizeEncodingName(name);



            EncodingInfoWrapper encInfo;

            if (CodecsInfo.Codecs.TryGetValue(name, out encInfo)) {

                encoding = (Encoding)encInfo.GetEncoding().Clone();

                return true;

            }

#endif

            encoding = null;

            return false;

        }



        internal static string RawUnicodeEscapeEncode(string s) {

            // in the common case we don't need to encode anything, so we

            // lazily create the StringBuilder only if necessary.

            StringBuilder b = null;

            for (int i = 0; i < s.Length; i++) {

                char ch = s[i];

                if (ch > 0xff) {

                    ReprInit(ref b, s, i);

                    b.AppendFormat("\\u{0:x4}", (int)ch);

                } else if (b != null) {

                    b.Append(ch);

                }

            }



            if (b == null) return s;

            return b.ToString();

        }





        #endregion



        #region Private implementation details



        private static int CheckIndex(object index, int defaultValue) {

            int res;



            if (index == null) {

                res = defaultValue;

            } else if (!Converter.TryConvertToIndex(index, out res)) {

                throw PythonOps.TypeError("slice indices must be integers or None or have an __index__ method");

            }



            return res;

        }



        private static void AppendJoin(object value, int index, StringBuilder sb) {

            string strVal;



            if ((strVal = value as string) != null) {

                sb.Append(strVal);

            } else if (Converter.TryConvertToString(value, out strVal) && strVal != null) {

                sb.Append(strVal);

            } else {

                throw PythonOps.TypeError("sequence item {0}: expected string, {1} found", index.ToString(), PythonOps.GetPythonTypeName(value));

            }

        }



        private static string ReplaceEmpty(string self, string new_, int maxsplit) {

            string v = self;



            if (maxsplit == 0) return v;

            else if (maxsplit < 0) maxsplit = v.Length + 1;

            else if (maxsplit > v.Length + 1) maxsplit = checked(v.Length + 1);

            

            int newLength = checked(v.Length + new_.Length * maxsplit);

            int max = Math.Min(v.Length, maxsplit);

            StringBuilder ret = new StringBuilder(newLength);

            for (int i = 0; i < max; i++) {

                ret.Append(new_);

                ret.Append(v[i]);

            }

            if (maxsplit > max) {

                ret.Append(new_);

            } else {

                ret.Append(v, max, v.Length - max);

            }



            return ret.ToString();

        }



        private static string Reverse(string s) {

            if (s.Length == 0 || s.Length == 1) return s;

            char[] rchars = new char[s.Length];

            for (int i = s.Length - 1, j = 0; i >= 0; i--, j++) {

                rchars[j] = s[i];

            }

            return new string(rchars);

        }



        internal static string ReprEncode(string s, char quote, ref bool isUnicode) {

            // in the common case we don't need to encode anything, so we

            // lazily create the StringBuilder only if necessary.

            StringBuilder b = null;

            for (int i = 0; i < s.Length; i++) {

                char ch = s[i];



                if (ch >= LowestUnicodeValue) isUnicode = true;

                switch (ch) {

                    case '\\': ReprInit(ref b, s, i); b.Append("\\\\"); break;

                    case '\t': ReprInit(ref b, s, i); b.Append("\\t"); break;

                    case '\n': ReprInit(ref b, s, i); b.Append("\\n"); break;

                    case '\r': ReprInit(ref b, s, i); b.Append("\\r"); break;

                    default:

                        if (quote != 0 && ch == quote) {

                            ReprInit(ref b, s, i);

                            b.Append('\\'); b.Append(ch);

                        } else if (ch < ' ' || (ch >= 0x7f && ch <= 0xff)) {

                            ReprInit(ref b, s, i);

                            b.AppendFormat("\\x{0:x2}", (int)ch);

                        } else if (ch > 0xff) {

                            ReprInit(ref b, s, i);

                            b.AppendFormat("\\u{0:x4}", (int)ch);

                        } else if (b != null) {

                            b.Append(ch);

                        }

                        break;

                }

            }



            if (b == null) return s;

            return b.ToString();

        }



        private static void ReprInit(ref StringBuilder sb, string s, int c) {

            if (sb != null) return;



            sb = new StringBuilder(s, 0, c, s.Length);

        }



        private static bool IsSign(char ch) {

            return ch == '+' || ch == '-';

        }



        internal static string GetEncodingName(Encoding encoding) {

#if !SILVERLIGHT

            string name = null;



            // if we have a valid code page try and get a reasonable name.  The

            // web names / mail displays match tend to CPython's terse names

            if (encoding.CodePage != 0) {

                if (encoding.IsBrowserDisplay) {

                    name = encoding.WebName;

                }



                if (name == null && encoding.IsMailNewsDisplay) {

                    name = encoding.HeaderName;

                }



                // otherwise use a code page number which also matches CPython               

                if (name == null) {

                    name = "cp" + encoding.CodePage;

                }

            }



            if (name == null) {

                // otherwise just finally fall back to the human readable name

                name = encoding.EncodingName;

            }

#else

            // Silverlight only has web names

            string name = encoding.WebName;

#endif



            return NormalizeEncodingName(name);

        }



        internal static string NormalizeEncodingName(string name) {

            if (name == null) {

                return null;

            }

            return name.ToLower(CultureInfo.InvariantCulture).Replace('-', '_').Replace(' ', '_');

        }



        private static string RawDecode(CodeContext/*!*/ context, string s, object encodingType, string errors) {

            PythonContext pc = PythonContext.GetContext(context);



            Encoding e = null;

            string encoding = encodingType as string;

            if (encoding == null) {

                e = encodingType as Encoding;

                if (e == null) {

                    if (encodingType == Missing.Value) {

                        encoding = pc.GetDefaultEncodingName();

                    } else {

                        throw PythonOps.TypeError("decode() expected string, got '{0}'", DynamicHelpers.GetPythonType(encodingType).Name);

                    }

                }

            }



            if (e == null) {

                string normalizedName = NormalizeEncodingName(encoding);

                if ("raw_unicode_escape" == normalizedName) {

                    return LiteralParser.ParseString(s, true, true);

                } else if ("unicode_escape" == normalizedName) {

                    return LiteralParser.ParseString(s, false, true);

                } else if ("string_escape" == normalizedName) {

                    return LiteralParser.ParseString(s, false, false);

                }

            }

            

            if (e != null || TryGetEncoding(encoding, out e)) {

                return DoDecode(context, s, errors, encoding, e);

            }



            // look for user-registered codecs

            PythonTuple codecTuple = PythonOps.LookupEncoding(context, encoding);

            if (codecTuple != null) {

                return UserDecodeOrEncode(codecTuple[/*Modules.PythonCodecs.DecoderIndex*/1], s);

            }



            throw PythonOps.LookupError("unknown encoding: {0}", encoding);

        }



        internal static string DoDecode(CodeContext context, string s, string errors, string encoding, Encoding e) {

#if !SILVERLIGHT // DecoderFallback

            // CLR's encoder exceptions have a 1-1 mapping w/ Python's encoder exceptions

            // so we just clone the encoding & set the fallback to throw in strict mode.

            e = (Encoding)e.Clone();



            switch (errors) {

                case "backslashreplace":

                case "xmlcharrefreplace":

                case "strict": e.DecoderFallback = DecoderFallback.ExceptionFallback; break;

                case "replace": e.DecoderFallback = DecoderFallback.ReplacementFallback; break;

                case "ignore":

                    e.DecoderFallback = new PythonDecoderFallback(encoding,

                        s,

                        null);

                    break;

                default:

                    e.DecoderFallback = new PythonDecoderFallback(encoding,

                        s,

                        PythonOps.LookupEncodingError(context, errors));

                    break;

            }

#endif



            byte[] bytes = s.MakeByteArray();

            int start = GetStartingOffset(e, bytes);



            return e.GetString(bytes, start, bytes.Length - start);

        }



        /// <summary>

        /// Gets the starting offset checking to see if the incoming bytes already include a preamble.

        /// </summary>

        private static int GetStartingOffset(Encoding e, byte[] bytes) {

            byte[] preamble = e.GetPreamble();

            int start = 0;

            if (bytes.Length >= preamble.Length) {

                bool differ = false;

                for (int i = 0; i < preamble.Length; i++) {

                    if (bytes[i] != preamble[i]) {

                        differ = true;

                    }

                }



                if (!differ) {

                    start = preamble.Length;

                }

            }

            return start;

        }



        private static string RawEncode(CodeContext/*!*/ context, string s, object encodingType, string errors) {

            string encoding = encodingType as string;

            Encoding e = null;

            if (encoding == null) {

                e = encodingType as Encoding;

                if (e == null) {

                    if (encodingType == Missing.Value) {

                        encoding = PythonContext.GetContext(context).GetDefaultEncodingName();

                    } else {

                        throw PythonOps.TypeError("encode() expected string, got '{0}'", DynamicHelpers.GetPythonType(encodingType).Name);

                    }

                }

            }



            if (e == null) {

                string normalizedName = NormalizeEncodingName(encoding);



                if ("raw_unicode_escape" == normalizedName) {

                    return RawUnicodeEscapeEncode(s);

                } else if ("unicode_escape" == normalizedName || "string_escape" == normalizedName) {

                    bool dummy = false;

                    return ReprEncode(s, '\'', ref dummy);

                }

            }



            if (e != null || TryGetEncoding(encoding, out e)) {

                return DoEncode(context, s, errors, encoding, e);

            }



                // look for user-registered codecs

            PythonTuple codecTuple = PythonOps.LookupEncoding(context, encoding);

            if (codecTuple != null) {

                return UserDecodeOrEncode(codecTuple[/*Modules.PythonCodecs.EncoderIndex*/0], s);

            }



            throw PythonOps.LookupError("unknown encoding: {0}", encoding);

        }



        internal static string DoEncode(CodeContext context, string s, string errors, string encoding, Encoding e) {

#if !SILVERLIGHT

            // CLR's encoder exceptions have a 1-1 mapping w/ Python's encoder exceptions

            // so we just clone the encoding & set the fallback to throw in strict mode

            e = (Encoding)e.Clone();



            switch (errors) {

                case "strict": e.EncoderFallback = EncoderFallback.ExceptionFallback; break;

                case "replace": e.EncoderFallback = EncoderFallback.ReplacementFallback; break;

                case "backslashreplace": e.EncoderFallback = new BackslashEncoderReplaceFallback(); break;

                case "xmlcharrefreplace": e.EncoderFallback = new XmlCharRefEncoderReplaceFallback(); break;

                case "ignore":

                    e.EncoderFallback = new PythonEncoderFallback(encoding,

                        s,

                        null);

                    break;

                default:

                    e.EncoderFallback = new PythonEncoderFallback(encoding,

                        s,

                        PythonOps.LookupEncodingError(context, errors));

                    break;

            }



#endif

            return PythonOps.MakeString(e.GetPreamble(), e.GetBytes(s));

        }





        private static string UserDecodeOrEncode(object function, string data) {

            object res = PythonCalls.Call(function, data);



            string strRes = AsString(res);

            if (strRes != null) return strRes;



            // tuple is string, bytes used, we just want the string...

            PythonTuple t = res as PythonTuple;

            if (t == null) throw PythonOps.TypeErrorForBadInstance("expected tuple, but found {0}", res);



            return Converter.ConvertToString(t[0]);

        }



#if !SILVERLIGHT

        static class CodecsInfo {

            public static readonly Dictionary<string, EncodingInfoWrapper> Codecs = MakeCodecsDict();



            private static Dictionary<string, EncodingInfoWrapper> MakeCodecsDict() {

                Dictionary<string, EncodingInfoWrapper> d = new Dictionary<string, EncodingInfoWrapper>();

                EncodingInfo[] encs = Encoding.GetEncodings();

                for (int i = 0; i < encs.Length; i++) {

                    string normalizedName = NormalizeEncodingName(encs[i].Name);



                    // setup well-known mappings, for everything

                    // else we'll store as lower case w/ _                

                    switch (normalizedName) {

                        case "us_ascii":

                            d["cp" + encs[i].CodePage.ToString()] = d[normalizedName] = d["us"] = d["ascii"] = d["646"] = d["us_ascii"] = new AsciiEncodingInfoWrapper();

                            continue;

                        case "iso_8859_1":

                            d["8859"] = d["latin_1"] = d["latin1"] = d["iso 8859_1"] = d["iso8859_1"] = d["cp819"] = d["819"] = d["latin"] = d["latin1"] = d["l1"] = encs[i];

                            break;

                        case "utf_7":

                            d["u7"] = d["unicode-1-1-utf-7"] = encs[i];

                            break;

                        case "utf_8":

                            d["utf_8_sig"] = encs[i];

                            d["utf_8"] = d["utf8"] = d["u8"] = new EncodingInfoWrapper(encs[i], new byte[0]);

                            continue;

                        case "utf_16":

                            d["utf_16_le"] = d["utf_16le"] = new EncodingInfoWrapper(encs[i], new byte[0]);

                            d["utf16"] = new EncodingInfoWrapper(encs[i], encs[i].GetEncoding().GetPreamble());

                            break;

                        case "unicodefffe": // big endian unicode                    

                            // strip off the pre-amble, CPython doesn't include it.

                            d["utf_16_be"] = d["utf_16be"] = new EncodingInfoWrapper(encs[i], new byte[0]);

                            break;

                    }



                    // publish under normalized name (all lower cases, -s replaced with _s)

                    d[normalizedName] = encs[i];

                    // publish under Windows code page as well...                

                    d["windows-" + encs[i].GetEncoding().WindowsCodePage.ToString()] = encs[i];

                    // publish under code page number as well...

                    d["cp" + encs[i].CodePage.ToString()] = d[encs[i].CodePage.ToString()] = encs[i];

                }



                d["raw_unicode_escape"] = new EncodingInfoWrapper(new UnicodeEscapeEncoding(true));

                d["unicode_escape"] = new EncodingInfoWrapper(new UnicodeEscapeEncoding(false));





#if DEBUG

                // all codecs should be stored in lowercase because we only look up from lowercase strings

                foreach (KeyValuePair<string, EncodingInfoWrapper> kvp in d) {

                    Debug.Assert(kvp.Key.ToLower(CultureInfo.InvariantCulture) == kvp.Key);

                }

#endif

                return d;

            }

        }



        class EncodingInfoWrapper {

            private EncodingInfo _info;

            private Encoding _encoding;

            private byte[] _preamble;



            public EncodingInfoWrapper(Encoding enc) {

                _encoding = enc;

            }



            public EncodingInfoWrapper(EncodingInfo info) {

                _info = info;

            }



            public EncodingInfoWrapper(EncodingInfo info, byte[] preamble) {

                _info = info;

                _preamble = preamble;

            }



            public virtual Encoding GetEncoding() {

                if(_encoding != null) return _encoding;



                if (_preamble == null) {

                    return _info.GetEncoding();

                }



                return new EncodingWrapper(_info.GetEncoding(), _preamble);

            }



            public static implicit operator EncodingInfoWrapper(EncodingInfo info) {

                return new EncodingInfoWrapper(info);

            }

        }



        class AsciiEncodingInfoWrapper : EncodingInfoWrapper {

            public AsciiEncodingInfoWrapper()

                : base((EncodingInfo)null) {

            }



            public override Encoding GetEncoding() {

                return PythonAsciiEncoding.Instance;

            }

        }

#endif



        class EncodingWrapper : Encoding {

            private byte[] _preamble;

            private Encoding _encoding;



            public EncodingWrapper(Encoding encoding, byte[] preamable) {

                _preamble = preamable;

                _encoding = encoding;

            }



            private void SetEncoderFallback() {

#if !SILVERLIGHT

                _encoding.EncoderFallback = EncoderFallback;

#endif

            }



            private void SetDecoderFallback() {

#if !SILVERLIGHT

                _encoding.DecoderFallback = DecoderFallback;

#endif

            }



            public override int GetByteCount(char[] chars, int index, int count) {

                SetEncoderFallback();

                return _encoding.GetByteCount(chars, index, count);

            }



            public override int GetBytes(char[] chars, int charIndex, int charCount, byte[] bytes, int byteIndex) {

                SetEncoderFallback();

                return _encoding.GetBytes(chars, charIndex, charCount, bytes, byteIndex);

            }



            public override int GetCharCount(byte[] bytes, int index, int count) {

                SetDecoderFallback();

                return _encoding.GetCharCount(bytes, index, count);

            }



            public override int GetChars(byte[] bytes, int byteIndex, int byteCount, char[] chars, int charIndex) {

                SetDecoderFallback();

                return _encoding.GetChars(bytes, byteIndex, byteCount, chars, charIndex);

            }



            public override int GetMaxByteCount(int charCount) {

                SetEncoderFallback();

                return _encoding.GetMaxByteCount(charCount);

            }



            public override int GetMaxCharCount(int byteCount) {

                SetDecoderFallback();

                return _encoding.GetMaxCharCount(byteCount);

            }



            public override byte[] GetPreamble() {

                return _preamble;

            }

            

            public override Encoder GetEncoder() {

                SetEncoderFallback();

                return _encoding.GetEncoder();

            }



            public override Decoder GetDecoder() {

                SetDecoderFallback();

                return _encoding.GetDecoder();

            }



            public override object Clone() {

                // need to call base.Clone to be marked as read/write

                EncodingWrapper res = (EncodingWrapper)base.Clone();

                res._encoding = (Encoding)_encoding.Clone();

                return res;

            }            

        }



        private static List SplitEmptyString(bool separators) {

            List ret = PythonOps.MakeEmptyList(1);

            if (separators) {

                ret.AddNoLock(String.Empty);

            }

            return ret;

        }



        private static List SplitInternal(string self, char[] seps, int maxsplit) {

            if (String.IsNullOrEmpty(self)) {

                return SplitEmptyString(seps != null);

            } else {

                string[] r = null;

                //  If the optional second argument sep is absent or None, the words are separated 

                //  by arbitrary strings of whitespace characters (space, tab, newline, return, formfeed);

                

                r = StringUtils.Split(self, seps, (maxsplit < 0) ? Int32.MaxValue : maxsplit + 1, 

                    (seps == null) ? StringSplitOptions.RemoveEmptyEntries : StringSplitOptions.None);



                List ret = PythonOps.MakeEmptyList(r.Length);

                foreach (string s in r) ret.AddNoLock(s);

                return ret;

            }

        }



        private static List SplitInternal(string self, string separator, int maxsplit) {

            if (String.IsNullOrEmpty(self)) {

                return SplitEmptyString(separator != null);

            } else {

                string[] r = StringUtils.Split(self, separator, (maxsplit < 0) ? Int32.MaxValue : maxsplit + 1, StringSplitOptions.None);



                List ret = PythonOps.MakeEmptyList(r.Length);

                foreach (string s in r) ret.AddNoLock(s);

                return ret;

            }

        }



        private static void TryStringOrTuple(object prefix) {

            if (prefix == null) {

                throw PythonOps.TypeError("expected string or Tuple, got NoneType");

            }

            if (!(prefix is string) && !(prefix is PythonTuple) && !(prefix is Extensible<string>)) {

                throw PythonOps.TypeError("expected string or Tuple, got {0} Type", prefix.GetType());

            }

        }



        private static string GetString(object obj) {

            string ret = AsString(obj);

            if (ret == null) {

                throw PythonOps.TypeError("expected string, got {0}", DynamicHelpers.GetPythonType(obj).Name);

            }

            return ret;

        }



        private static bool endswith(string self, string suffix) {

            return self.EndsWith(suffix);

        }



        //  Indexing is 0-based. Need to deal with negative indices

        //  (which mean count backwards from end of sequence)

        //  +---+---+---+---+---+ 

        //  | a | b | c | d | e |

        //  +---+---+---+---+---+ 

        //    0   1   2   3   4    

        //   -5  -4  -3  -2  -1



        private static bool endswith(string self, string suffix, int start) {

            int len = self.Length;

            if (start > len) return false;

            // map the negative indice to its positive counterpart

            if (start < 0) {

                start += len;

                if (start < 0) start = 0;

            }

            return self.Substring(start).EndsWith(suffix);

        }



        //  With optional start, test beginning at that position (the char at that index is

        //  included in the test). With optional end, stop comparing at that position (the 

        //  char at that index is not included in the test)

        private static bool endswith(string self, string suffix, int start, int end) {

            int len = self.Length;

            if (start > len) return false;

            // map the negative indices to their positive counterparts

            else if (start < 0) {

                start += len;

                if (start < 0) start = 0;

            }

            if (end >= len) return self.Substring(start).EndsWith(suffix);

            else if (end < 0) {

                end += len;

                if (end < 0) return false;

            }

            if (end < start) return false;

            return self.Substring(start, end - start).EndsWith(suffix);

        }





        private static bool endswith(string self, PythonTuple suffix) {

            foreach (object obj in suffix) {

                if (self.EndsWith(GetString(obj))) {

                    return true;

                }

            }

            return false;

        }



        private static bool endswith(string self, PythonTuple suffix, int start) {

            foreach (object obj in suffix) {

                if (endswith(self, GetString(obj), start)) {

                    return true;

                }

            }

            return false;

        }



        private static bool endswith(string self, PythonTuple suffix, int start, int end) {

            foreach (object obj in suffix) {

                if (endswith(self, GetString(obj), start, end)) {

                    return true;

                }

            }

            return false;

        }



        private static bool startswith(string self, string prefix) {

            return self.StartsWith(prefix);

        }



        private static bool startswith(string self, string prefix, int start) {

            int len = self.Length;

            if (start > len) return false;

            if (start < 0) {

                start += len;

                if (start < 0) start = 0;

            }

            return self.Substring(start).StartsWith(prefix);

        }



        private static bool startswith(string self, string prefix, int start, int end) {

            int len = self.Length;

            if (start > len) return false;

            // map the negative indices to their positive counterparts

            else if (start < 0) {

                start += len;

                if (start < 0) start = 0;

            }

            if (end >= len) return self.Substring(start).StartsWith(prefix);

            else if (end < 0) {

                end += len;

                if (end < 0) return false;

            }

            if (end < start) return false;

            return self.Substring(start, end - start).StartsWith(prefix);

        }



        private static bool startswith(string self, PythonTuple prefix) {

            foreach (object obj in prefix) {

                if (self.StartsWith(GetString(obj))) {

                    return true;

                }

            }

            return false;

        }



        private static bool startswith(string self, PythonTuple prefix, int start) {

            foreach (object obj in prefix) {

                if (startswith(self, GetString(obj), start)) {

                    return true;

                }

            }

            return false;

        }



        private static bool startswith(string self, PythonTuple prefix, int start, int end) {

            foreach (object obj in prefix) {

                if (startswith(self, GetString(obj), start, end)) {

                    return true;

                }

            }

            return false;

        }



        // note: any changes in how this iterator works should also be applied in the

        //       optimized overloads of Builtins.map()

        [PythonType("str_iterator")]

        private class PythonStringEnumerable : IEnumerable, IEnumerator<string> {

            private readonly string/*!*/ _s;

            private int _index;



            public PythonStringEnumerable(string s) {

                Assert.NotNull(s);



                _index = -1;

                _s = s;

            }



            #region IEnumerable Members



            public IEnumerator GetEnumerator() {

                return this;

            }



            #endregion



            #region IEnumerator<string> Members



            public string Current {

                get {

                    if (_index < 0) {

                        throw PythonOps.SystemError("Enumeration has not started. Call MoveNext.");

                    } else if (_index >= _s.Length) {

                        throw PythonOps.SystemError("Enumeration already finished.");

                    }

                    return ScriptingRuntimeHelpers.CharToString(_s[_index]);

                }

            }



            #endregion



            #region IDisposable Members



            public void Dispose() { }



            #endregion



            #region IEnumerator Members



            object IEnumerator.Current {

                get {

                    return ((IEnumerator<string>)this).Current;

                }

            }



            public bool MoveNext() {

                if (_index >= _s.Length) {

                    return false;

                }

                _index++;

                return _index != _s.Length;

            }



            public void Reset() {

                _index = -1;

            }



            #endregion

        }



        internal static IEnumerable StringEnumerable(string str) {

            return new PythonStringEnumerable(str);

        }



        internal static IEnumerator<string> StringEnumerator(string str) {

            return new PythonStringEnumerable(str);

        }



        #endregion



        #region  Unicode Encode/Decode Fallback Support



#if !SILVERLIGHT // EncoderFallbackBuffer

        /// When encoding or decoding strings if an error occurs CPython supports several different

        /// behaviors, in addition it supports user-extensible behaviors as well.  For the default

        /// behavior we're ok - both of us support throwing and replacing.  For custom behaviors

        /// we define a single fallback for decoding and encoding that calls the python function to do

        /// the replacement.

        /// 

        /// When we do the replacement we call the provided handler w/ a UnicodeEncodeError or UnicodeDecodeError

        /// object which contains:

        ///         encoding    (string, the encoding the user requested)

        ///         end         (the end of the invalid characters)

        ///         object      (the original string being decoded)

        ///         reason      (the error, e.g. 'unexpected byte code', not sure of others)

        ///         start       (the start of the invalid sequence)

        ///         

        /// The decoder returns a tuple of (unicode, int) where unicode is the replacement string

        /// and int is an index where encoding should continue.



        private class PythonEncoderFallbackBuffer : EncoderFallbackBuffer {

            private object _function;

            private string _encoding, _strData;

            private string _buffer;

            private int _bufferIndex;



            public PythonEncoderFallbackBuffer(string encoding, string str, object callable) {

                _function = callable;

                _strData = str;

                this._encoding = encoding;

            }



            public override bool Fallback(char charUnknown, int index) {

                return DoPythonFallback(index, 1);

            }



            public override bool Fallback(char charUnknownHigh, char charUnknownLow, int index) {

                return DoPythonFallback(index, 2);

            }



            public override char GetNextChar() {

                if (_buffer == null || _bufferIndex >= _buffer.Length) return Char.MinValue;



                return _buffer[_bufferIndex++];

            }



            public override bool MovePrevious() {

                if (_bufferIndex > 0) {

                    _bufferIndex--;

                    return true;

                }

                return false;

            }



            public override int Remaining {

                get {

                    if (_buffer == null) return 0;

                    return _buffer.Length - _bufferIndex;

                }

            }



            public override void Reset() {

                _buffer = null;

                _bufferIndex = 0;

                base.Reset();

            }



            private bool DoPythonFallback(int index, int length) {

                if (_function != null) {

                    // create the exception object to hand to the user-function...

                    PythonExceptions._UnicodeEncodeError exObj = new PythonExceptions._UnicodeEncodeError();



                    exObj.__init__(_encoding, _strData, index, index + length, "unexpected code byte");



                    // call the user function...

                    object res = PythonCalls.Call(_function, exObj);



                    string replacement = PythonDecoderFallbackBuffer.CheckReplacementTuple(res, "encoding");



                    // finally process the user's request.

                    _buffer = replacement;

                    _bufferIndex = 0;

                    return true;

                }



                return false;                

            }



        }



        class PythonEncoderFallback : EncoderFallback {

            private object _function;

            private string _str;

            private string _enc;



            public PythonEncoderFallback(string encoding, string data, object callable) {

                _function = callable;

                _str = data;

                _enc = encoding;

            }



            public override EncoderFallbackBuffer CreateFallbackBuffer() {

                return new PythonEncoderFallbackBuffer(_enc, _str, _function);

            }



            public override int MaxCharCount {

                get { return Int32.MaxValue; }

            }

        }



        private class PythonDecoderFallbackBuffer : DecoderFallbackBuffer {

            private object _function;

            private string _encoding, _strData;

            private string _buffer;

            private int _bufferIndex;



            public PythonDecoderFallbackBuffer(string encoding, string str, object callable) {

                this._encoding = encoding;

                this._strData = str;

                this._function = callable;

            }



            public override int Remaining {

                get {

                    if (_buffer == null) return 0;

                    return _buffer.Length - _bufferIndex;

                }

            }

            

            public override char GetNextChar() {

                if (_buffer == null || _bufferIndex >= _buffer.Length) return Char.MinValue;



                return _buffer[_bufferIndex++];

            }



            public override bool MovePrevious() {

                if (_bufferIndex > 0) {

                    _bufferIndex--;

                    return true;

                }

                return false;

            }



            public override void Reset() {

                _buffer = null;

                _bufferIndex = 0;

                base.Reset();

            }



            public override bool Fallback(byte[] bytesUnknown, int index) {

                if (_function != null) {

                    // create the exception object to hand to the user-function...

                    PythonExceptions._UnicodeDecodeError exObj = new PythonExceptions._UnicodeDecodeError();



                    exObj.__init__(_encoding, _strData, index, index + bytesUnknown.Length, "unexpected code byte");



                    // call the user function...

                    object res = PythonCalls.Call(_function, exObj);



                    string replacement = CheckReplacementTuple(res, "decoding");



                    // finally process the user's request.

                    _buffer = replacement;

                    _bufferIndex = 0;

                    return true;

                }



                return false;

            }



            internal static string CheckReplacementTuple(object res, string encodeOrDecode) {

                bool ok = true;

                string replacement = null;

                PythonTuple tres = res as PythonTuple;



                // verify the result is sane...

                if (tres != null && tres.__len__() == 2) {

                    if (!Converter.TryConvertToString(tres[0], out replacement)) ok = false;

                    if (ok) {

                        int bytesSkipped;

                        if (!Converter.TryConvertToInt32(tres[1], out bytesSkipped)) ok = false;

                    }

                } else {

                    ok = false;

                }



                if (!ok) throw PythonOps.TypeError("{1} error handler must return tuple containing (str, int), got {0}", PythonOps.GetPythonTypeName(res), encodeOrDecode);

                return replacement;

            }

        }



        class PythonDecoderFallback : DecoderFallback {

            private object function;

            private string str;

            private string enc;



            public PythonDecoderFallback(string encoding, string data, object callable) {

                function = callable;

                str = data;

                enc = encoding;

            }



            public override DecoderFallbackBuffer CreateFallbackBuffer() {

                return new PythonDecoderFallbackBuffer(enc, str, function);

            }



            public override int MaxCharCount {

                get { throw new NotImplementedException(); }

            }

        }



        class BackslashEncoderReplaceFallback : EncoderFallback {

            class BackslashReplaceFallbackBuffer : EncoderFallbackBuffer {

                private List<char> _buffer = new List<char>();

                private int _index;



                public override bool Fallback(char charUnknownHigh, char charUnknownLow, int index) {

                    return false;

                }



                public override bool Fallback(char charUnknown, int index) {

                    _buffer.Add('\\');

                    int val = (int)charUnknown;

                    if (val > 0xFF) {

                        _buffer.Add('u');

                        AddCharacter(val >> 8);

                        AddCharacter(val & 0xFF);

                    } else {

                        _buffer.Add('x');

                        AddCharacter(charUnknown);

                    }

                    return true;

                }



                private void AddCharacter(int val) {

                    AddOneDigit(((val) & 0xF0) >> 4);

                    AddOneDigit(val & 0x0F);

                }



                private void AddOneDigit(int val) {

                    if (val > 9) {

                        _buffer.Add((char)('a' + val - 0x0A));

                    } else {

                        _buffer.Add((char)('0' + val));

                    }

                }



                public override char GetNextChar() {

                    if (_index == _buffer.Count) return Char.MinValue;



                    return _buffer[_index++];

                }



                public override bool MovePrevious() {

                    if (_index > 0) {

                        _index--;

                        return true;

                    }

                    return false;

                }



                public override int Remaining {

                    get { return _buffer.Count - _index; }

                }

            }



            public override EncoderFallbackBuffer CreateFallbackBuffer() {

                return new BackslashReplaceFallbackBuffer();

            }



            public override int MaxCharCount {

                get { throw new NotImplementedException(); }

            }

        }



        class XmlCharRefEncoderReplaceFallback : EncoderFallback {

            class XmlCharRefEncoderReplaceFallbackBuffer : EncoderFallbackBuffer {

                private List<char> _buffer = new List<char>();

                private int _index;



                public override bool Fallback(char charUnknownHigh, char charUnknownLow, int index) {

                    return false;

                }



                public override bool Fallback(char charUnknown, int index) {

                    _buffer.Add('&');

                    _buffer.Add('#');

                    int val = (int)charUnknown;

                    foreach (char c in val.ToString()) {

                        _buffer.Add(c);

                    }

                    _buffer.Add(';');

                    return true;

                }



                public override char GetNextChar() {

                    if (_index == _buffer.Count) return Char.MinValue;



                    return _buffer[_index++];

                }



                public override bool MovePrevious() {

                    if (_index > 0) {

                        _index--;

                        return true;

                    }

                    return false;

                }



                public override int Remaining {

                    get { return _buffer.Count - _index; }

                }

            }



            public override EncoderFallbackBuffer CreateFallbackBuffer() {

                return new XmlCharRefEncoderReplaceFallbackBuffer();

            }



            public override int MaxCharCount {

                get { throw new NotImplementedException(); }

            }

        }



        class UnicodeEscapeEncoding : Encoding {

            private bool _raw;



            public UnicodeEscapeEncoding(bool raw) {

                _raw = raw;

            }

            

            public override int GetByteCount(char[] chars, int index, int count) {

                return EscapeEncode(chars, index, count).Length;

            }



            private string EscapeEncode(char[] chars, int index, int count) {

                if (_raw) {

                    return RawUnicodeEscapeEncode(new string(chars, index, count));

                }



                bool dummy = false;

                return ReprEncode(new string(chars, index, count), ref dummy);

            }



            public override int GetBytes(char[] chars, int charIndex, int charCount, byte[] bytes, int byteIndex) {

                if (_raw) {

                    string res = RawUnicodeEscapeEncode(new string(chars, charIndex, charCount));

                    for (int i = 0; i < res.Length; i++) {

                        bytes[i + byteIndex] = _raw ? (byte)res[i] : (byte)chars[i];

                    }

                    return res.Length;

                } else {                    

                    for (int i = 0; i < charCount; i++) {

                        bytes[i + byteIndex] = (byte)chars[i + charIndex];

                    }

                    return charCount;

                }

            }



            public override int GetCharCount(byte[] bytes, int index, int count) {

                StringBuilder builder = new StringBuilder();

                for (int i = 0; i < count; i++) {

                    builder.Append((char)bytes[i + index]);

                }



                return LiteralParser.ParseString(builder.ToString(), _raw, true).Length;

            }



            public override int GetChars(byte[] bytes, int byteIndex, int byteCount, char[] chars, int charIndex) {

                StringBuilder builder = new StringBuilder();

                for (int i = 0; i < byteCount; i++) {

                    builder.Append((char)bytes[i + byteIndex]);

                }



                string res = LiteralParser.ParseString(builder.ToString(), _raw, true);

                for (int i = 0; i < res.Length; i++) {

                    chars[i + charIndex] = (char)res[i];

                }



                return res.Length;

            }



            public override int GetMaxByteCount(int charCount) {

                return charCount * 5;

            }



            public override int GetMaxCharCount(int byteCount) {

                return byteCount;

            }

        }

#endif

        #endregion



        public static string/*!*/ __repr__(string/*!*/ self) {

            return StringOps.Quote(self);

        }



    }

}