/Languages/IronPython/IronPython/Runtime/Operations/StringOps.cs

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/* ****************************************************************************
 *
 * Copyright (c) Microsoft Corporation. 
 *
 * This source code is subject to terms and conditions of the Apache License, Version 2.0. A 
 * copy of the license can be found in the License.html file at the root of this distribution. If 
 * you cannot locate the  Apache License, Version 2.0, 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 Apache License, Version 2.0.
 *
 * 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 FEATURE_NUMERICS
using System.Numerics;
#else
using Microsoft.Scripting.Math;
#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);
            else if (value is Bytes) return Value.Contains(value.ToString());

            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;

        internal static object FastNew(CodeContext/*!*/ context, object x) {
            if (x == null) {
                return "None";
            }

            string xstr = (x as string);
            if (xstr != null) {
                return xstr;
            }

            // 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");
        }

        #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 @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 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, [BytesConversion]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, [BytesConversion]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.ToUpperInvariant(self[0]) + self.Substring(1).ToLowerInvariant();
        }

        //  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, [BytesConversion]string sub) {
            return count(self, sub, 0, self.Length);
        }

        public static int count(this string self, [BytesConversion]string sub, int start) {
            return count(self, sub, start, self.Length);
        }

        public static int count(this string self, [BytesConversion]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, [BytesConversion]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, [BytesConversion]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, [BytesConversion]string sub, BigInteger start) {
            if (sub == null) throw PythonOps.TypeError("expected string, got NoneType");
            if (start > self.Length) return -1;
            return find(self, sub, (int)start);
        }

        public static int find(this string self, [BytesConversion]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, [BytesConversion]string sub, BigInteger start, BigInteger end) {
            if (sub == null) throw PythonOps.TypeError("expected string, got NoneType");
            if (start > self.Length) return -1;
            return find(self, sub, (int)start, (int)end);
        }

        public static int find(this string self, [BytesConversion]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, [BytesConversion]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, [BytesConversion]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, [BytesConversion]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, [BytesConversion]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--) {
                // CPython considers the circled digits to be digits
                if (!Char.IsDigit(v, i) && (v[i] < '\u2460' || v[i] > '\u2468')) 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) || CharUnicodeInfo.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 sequence 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();
        }

        // required for better match with cpython upper/lower
        private static CultureInfo CasingCultureInfo = new CultureInfo("en");

        public static string lower(this string self) {
            return CasingCultureInfo.TextInfo.ToLower(self);
        }

        internal static string ToLowerAsciiTriggered(this string self) {
            for (int i = 0; i < self.Length; i++) {
                if (self[i] >= 'A' && self[i] <= 'Z') {
                    return self.ToLowerInvariant();
                }
            }
            return self;
        }

        public static string lstrip(this string self) {
            return self.TrimStart();
        }

        public static string lstrip(this string self, [BytesConversion]string chars) {
            if (chars == null) return lstrip(self);
            return self.TrimStart(chars.ToCharArray());
        }

        [return: SequenceTypeInfo(typeof(string))]
        public static PythonTuple partition(this string self, [BytesConversion]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);
        }

        public static string replace(this string self, [BytesConversion]string old, [BytesConversion]string @new,
            [DefaultParameterValue(-1)]int count) {

            if (old == null) {
                throw PythonOps.TypeError("expected a character buffer object"); // cpython message
            }
            if (old.Length == 0) return ReplaceEmpty(self, @new, count);

            string v = self;
            int replacements = StringOps.count(v, old);
            replacements = (count < 0 || count > replacements) ? replacements : count;
            int newLength = v.Length;
            newLength -= replacements * old.Length;
            newLength = checked(newLength + replacements * @new.Length);
            StringBuilder ret = new StringBuilder(newLength);

            int index;
            int start = 0;
            while (count != 0 && (index = v.IndexOf(old, start, StringComparison.Ordinal)) != -1) {
                ret.Append(v, start, index - start);
                ret.Append(@new);
                start = index + old.Length;
                count--;
            }
            ret.Append(v.Substring(start));

            return ret.ToString();
        }

        public static int rfind(this string self, [BytesConversion]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, [BytesConversion]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, [BytesConversion]string sub, BigInteger start) {
            if (sub == null) throw PythonOps.TypeError("expected string, got NoneType");
            if (start > self.Length) return -1;
            return rfind(self, sub, (int)start, self.Length);
        }

        public static int rfind(this string self, [BytesConversion]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, [BytesConversion]string sub, BigInteger start, BigInteger end) {
            if (sub == null) throw PythonOps.TypeError("expected string, got NoneType");
            if (start > self.Length) return -1;
            return rfind(self, sub, (int)start, (int)end);
        }

        public static int rfind(this string self, [BytesConversion]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, [BytesConversion]string sub) {
            return rindex(self, sub, 0, self.Length);
        }

        public static int rindex(this string self, [BytesConversion]string sub, int start) {
            return rindex(self, sub, start, self.Length);
        }

        public static int rindex(this string self, [BytesConversion]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, [BytesConversion]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();
        }

        [return: SequenceTypeInfo(typeof(string))]
        public static PythonTuple rpartition(this string self, [BytesConversion]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, [BytesConversion]string sep) {
            return rsplit(self, sep, -1);
        }

        public static List rsplit(this string self, [BytesConversion]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();
        }

        public static string rstrip(this string self, [BytesConversion]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, [BytesConversion]string sep) {
            return split(self, sep, -1);
        }

        public static List split(this string self, [BytesConversion]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, [BytesConversion]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.ToLowerInvariant(ch);
                else if (Char.IsLower(ch)) ret[i] = Char.ToUpperInvariant(ch);
            }
            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.ToUpperInvariant(retchars[i]);
                    else
                        retchars[i] = Char.ToLowerInvariant(retchars[i]);
                    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)) {
                    var mapped = table[idx];
                    if (mapped == null) {
                        continue;
                    }
                    if (mapped is int) {
                        var mappedInt = (int) mapped;
                        if (mappedInt > 0xFFFF) {
                            throw PythonOps.TypeError("character mapping must be in range(0x%lx)");
                        }
                        ret.Append((char)(int)mapped);
                    } else if (mapped is String) {
                        ret.Append(mapped);
                    } else {
                        throw PythonOps.TypeError("character mapping must return integer, None or unicode");
                    }
                } else {
                    ret.Append(self[i]);
                }
            }
            return ret.ToString();
        }

        public static string translate(this string self, [BytesConversion]string table) {
            return translate(self, table, (string)null);
        }

        public static string translate(this string self, [BytesConversion]string table, [BytesConversion]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 CasingCultureInfo.TextInfo.ToUpper(self);
        }

        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 &&…