Python 2.3 Quick Reference


 25 Jan 2003  upgraded by Raymond Hettinger for Python 2.3
 16 May 2001  upgraded by Richard Gruet and Simon Brunning for Python 2.0
 2000/07/18  upgraded by Richard Gruet, rgruet@intraware.com for Python 1.5.2
from V1.3 ref
1995/10/30, by Chris Hoffmann, choffman@vicorp.com

Based on:
    Python Bestiary, Author: Ken Manheimer, ken.manheimer@nist.gov
    Python manuals, Authors: Guido van Rossum and Fred Drake
    What's new in Python 2.0, Authors: A.M. Kuchling and Moshe Zadka
    python-mode.el, Author: Tim Peters, tim_one@email.msn.com

    and the readers of comp.lang.python

Python's nest: http://www.python.org     Developement: http://
python.sourceforge.net/    ActivePython : http://www.ActiveState.com/ASPN/
Python/
newsgroup: comp.lang.python  Help desk: help@python.org
Resources: http://starship.python.net/
           http://www.vex.net/parnassus/
           http://aspn.activestate.com/ASPN/Cookbook/Python
FAQ:       http://www.python.org/cgi-bin/faqw.py
Full documentation: http://www.python.org/doc/
Excellent reference books:
           Python Essential Reference by David Beazley (New Riders)
           Python Pocket Reference by Mark Lutz (O'Reilly)


Invocation Options

python [-diOStuUvxX?] [-c command | script | - ] [args]

                              Invocation Options
Option                                  Effect
-c cmd  program passed in as string (terminates option list)
-d      Outputs parser debugging information (also PYTHONDEBUG=x)
-E      ignore environment variables (such as PYTHONPATH)
-h      print this help message and exit
-i      Inspect interactively after running script (also PYTHONINSPECT=x) and
        force prompts, even if stdin appears not to be a terminal
-m mod  run library module as a script (terminates option list
-O      optimize generated bytecode (a tad; also PYTHONOPTIMIZE=x)
-OO     remove doc-strings in addition to the -O optimizations
-Q arg  division options: -Qold (default), -Qwarn, -Qwarnall, -Qnew
-S      Don't perform 'import site' on initialization
-t      Issue warnings about inconsistent tab usage (-tt: issue errors)
-u      Unbuffered binary stdout and stderr (also PYTHONUNBUFFERED=x).
-v      Verbose (trace import statements) (also PYTHONVERBOSE=x)
-W arg : warning control (arg is action:message:category:module:lineno)
-x      Skip first line of source, allowing use of non-unix Forms of #!cmd
-?      Help!
-3      warn about Python 3.x incompatibilities
-c      Specify the command to execute (see next section). This terminates the
command option list (following options are passed as arguments to the command).
        the name of a python file (.py) to execute read from stdin.
script  Anything afterward is passed as options to python script or command,
        not interpreted as an option to interpreter itself.
args    passed to script or command (in sys.argv[1:])
        If no script or command, Python enters interactive mode.

  * Available IDEs in std distrib: IDLE (tkinter based, portable), Pythonwin
    (Windows).



Environment variables

                             Environment variables
    Variable                                 Effect
PYTHONHOME       Alternate prefix directory (or prefix;exec_prefix). The
                 default module search path uses prefix/lib
                 Augments the default search path for module files. The format
                 is the same as the shell's $PATH: one or more directory
                 pathnames separated by ':' or ';' without spaces around
                 (semi-)colons!
PYTHONPATH       On Windows first search for Registry key HKEY_LOCAL_MACHINE\
                 Software\Python\PythonCore\x.y\PythonPath (default value). You
                 may also define a key named after your application with a
                 default string value giving the root directory path of your
                 app.
                 If this is the name of a readable file, the Python commands in
PYTHONSTARTUP    that file are executed before the first prompt is displayed in
                 interactive mode (no default).
PYTHONDEBUG      If non-empty, same as -d option
PYTHONINSPECT    If non-empty, same as -i option
PYTHONSUPPRESS   If non-empty, same as -s option
PYTHONUNBUFFERED If non-empty, same as -u option
PYTHONVERBOSE    If non-empty, same as -v option
PYTHONCASEOK     If non-empty, ignore case in file/module names (imports)




Notable lexical entities

Keywords

    and       del       for       is        raise
    assert    elif      from      lambda    return
    break     else      global    not       try
    class     except    if        or        while
    continue  exec      import    pass      yield
    def       finally   in        print

  * (list of keywords in std module: keyword)
  * Illegitimate Tokens (only valid in strings): @ $ ?
  * A statement must all be on a single line. To break a statement over
    multiple lines use "\", as with the C preprocessor.
    Exception: can always break when inside any (), [], or {} pair, or in
    triple-quoted strings.
  * More than one statement can appear on a line if they are separated with
    semicolons (";").
  * Comments start with "#" and continue to end of line.

Identifiers

        (letter | "_")  (letter | digit | "_")*

  * Python identifiers keywords, attributes, etc. are case-sensitive.
  * Special forms: _ident (not imported by 'from module import *'); __ident__
    (system defined name);
               __ident (class-private name mangling)

Strings

    "a string enclosed by double quotes"
    'another string delimited by single quotes and with a " inside'
    '''a string containing embedded newlines and quote (') marks, can be
    delimited with triple quotes.'''
    """ may also use 3- double quotes as delimiters """
    u'a unicode string'   U"Another unicode string"
    r'a raw string where \ are kept (literalized): handy for regular
    expressions and windows paths!'
    R"another raw string"    -- raw strings cannot end with a \
    ur'a unicode raw string'   UR"another raw unicode"

        Use \ at end of line to continue a string on next line.
        adjacent strings are concatened, e.g. 'Monty' ' Python' is the same as
        'Monty Python'.
        u'hello' + ' world'  --> u'hello world'   (coerced to unicode)

    String Literal Escapes

     \newline  Ignored (escape newline)
     \\ Backslash (\)        \e Escape (ESC)        \v Vertical Tab (VT)
     \' Single quote (')     \f Formfeed (FF)       \OOO char with octal value OOO
     \" Double quote (")     \n Linefeed (LF)
     \a Bell (BEL)           \r Carriage Return (CR) \xHH  char with hex value HH
     \b Backspace (BS)       \t Horizontal Tab (TAB)
     \uHHHH  unicode char with hex value HHHH, can only be used in unicode string
     \UHHHHHHHH  unicode char with hex value HHHHHHHH, can only be used in unicode string
     \AnyOtherChar is left as-is

  * NUL byte (\000) is NOT an end-of-string marker; NULs may be embedded in
    strings.
  * Strings (and tuples) are immutable: they cannot be modified.

Numbers

    Decimal integer: 1234, 1234567890546378940L        (or l)
    Octal integer: 0177, 0177777777777777777 (begin with a 0)
    Hex integer: 0xFF, 0XFFFFffffFFFFFFFFFF (begin with 0x or 0X)
    Long integer (unlimited precision): 1234567890123456
    Float (double precision): 3.14e-10, .001, 10., 1E3
    Complex: 1J, 2+3J, 4+5j (ends with J or j, + separates (float) real and
    imaginary parts)

Sequences

  * String of length 0, 1, 2 (see above)
    '', '1', "12", 'hello\n'
  * Tuple of length 0, 1, 2, etc:
    () (1,) (1,2)     # parentheses are optional if len > 0
  * List of length 0, 1, 2, etc:
    [] [1] [1,2]

Indexing is 0-based. Negative indices (usually) mean count backwards from end
of sequence.

Sequence slicing [starting-at-index : but-less-than-index]. Start defaults to
'0'; End defaults to 'sequence-length'.

a = (0,1,2,3,4,5,6,7)
    a[3] ==> 3
    a[-1] ==> 7
    a[2:4] ==> (2, 3)
    a[1:] ==> (1, 2, 3, 4, 5, 6, 7)
    a[:3] ==> (0, 1, 2)
    a[:] ==> (0,1,2,3,4,5,6,7)  # makes a copy of the sequence.

Dictionaries (Mappings)

    {}                              # Zero length empty dictionary
    {1 : 'first'}                   # Dictionary with one (key, value) pair
    {1 : 'first',  'next': 'second'}
    dict([('one',1),('two',2)])     # Construct a dict from an item list
    dict('one'=1, 'two'=2)          # Construct a dict using keyword args
    dict.fromkeys(['one', 'keys'])  # Construct a dict from a sequence

Operators and their evaluation order

                     Operators and their evaluation order
Highest             Operator                             Comment
        (...) [...] {...} `...`           Tuple, list & dict. creation; string
                                          conv.
        s[i]  s[i:j]  s.attr f(...)       indexing & slicing; attributes, fct
                                          calls
        +x, -x, ~x                        Unary operators
        x**y                              Power
        x*y  x/y  x%y x//y                mult, division, modulo, floor division
        x+y  x-y                          addition, subtraction
        x<<y   x>>y                       Bit shifting
        x&y                               Bitwise and
        x^y                               Bitwise exclusive or
        x|y                               Bitwise or
        x<y  x<=y  x>y  x>=y  x==y x!=y   Comparison,
        x<>y                              identity,
        x is y   x is not y               membership
        x in s   x not in s
        not x                             boolean negation
        x and y                           boolean and
        x or y                            boolean or
Lowest  lambda args: expr                 anonymous function

Alternate names are defined in module operator (e.g. __add__ and add for +)
Most operators are overridable.

Many binary operators also support augmented assignment:
        x += 1                            # Same as x = x + 1


Basic Types and Their Operations

Comparisons (defined between *any* types)

               Comparisons
Comparison         Meaning          Notes
<          strictly less than        (1)
<=         less than or equal to
>          strictly greater than
>=         greater than or equal to
==         equal to
!= or <>   not equal to
is         object identity           (2)
is not     negated object identity   (2)

Notes :
    Comparison behavior can be overridden for a given class by defining special
method __cmp__.
    The above comparisons return True or False which are of type bool
(a subclass of int) and behave exactly as 1 or 0 except for their type and
that they print as True or False instead of 1 or 0.
    (1) X < Y < Z < W has expected meaning, unlike C
    (2) Compare object identities (i.e. id(object)), not object values.

Boolean values and operators

                         Boolean values and operators
              Value or Operator                         Returns           Notes
None, numeric zeros, empty sequences and      False
mappings
all other values                              True
not x                                         True if x is False, else
                                              True
x or y                                        if x is False then y, else   (1)
                                              x
x and y                                       if x is False then x, else   (1)
                                              y

Notes :
    Truth testing behavior can be overridden for a given class by defining
special method __nonzero__.
    (1) Evaluate second arg only if necessary to determine outcome.

None

    None is used as default return value on functions. Built-in single object
    with type NoneType.
    Input that evaluates to None does not print when running Python
    interactively.

Numeric types

Floats, integers and long integers.

    Floats are implemented with C doubles.
    Integers are implemented with C longs.
    Long integers have unlimited size (only limit is system resources)

Operators on all numeric types

           Operators on all numeric types
 Operation                    Result
abs(x)       the absolute value of x
int(x)       x converted to integer
long(x)      x converted to long integer
float(x)     x converted to floating point
-x           x negated
+x           x unchanged
x + y        the sum of x and y
x - y        difference of x and y
x * y        product of x and y
x / y        quotient of x and y
x % y        remainder of x / y
divmod(x, y) the tuple (x/y, x%y)
x ** y       x to the power y (the same as pow(x, y))

Bit operators on integers and long integers

              Bit operators
Operation             >Result
~x        the bits of x inverted
x ^ y     bitwise exclusive or of x and y
x & y     bitwise and of x and y
x | y     bitwise or of x and y
x << n    x shifted left by n bits
x >> n    x shifted right by n bits

Complex Numbers

  * represented as a pair of machine-level double precision floating point
    numbers.
  * The real and imaginary value of a complex number z can be retrieved through
    the attributes z.real and z.imag.

Numeric exceptions

TypeError
    raised on application of arithmetic operation to non-number
OverflowError
     numeric bounds exceeded
ZeroDivisionError
     raised when zero second argument of div or modulo op
FloatingPointError
     raised when a floating point operation fails

Operations on all sequence types (lists, tuples, strings)

                Operations on all sequence types
Operation                     Result                     Notes
x in s     True if an item of s is equal to x, else False
x not in s False if an item of s is equal to x, else True
for x in s: loops over the sequence
s + t      the concatenation of s and t
s * n, n*s n copies of s concatenated
s[i]       i'th item of s, origin 0                       (1)
s[i:j]     slice of s from i (included) to j (excluded) (1), (2)
len(s)     length of s
min(s)     smallest item of s
max(s)     largest item of (s)
iter(s)    returns an iterator over s.  iterators define __iter__ and next()

Notes :
    (1) if i or j is negative, the index is relative to the end of the string,
ie len(s)+ i or len(s)+j is
         substituted. But note that -0 is still 0.
    (2) The slice of s from i to j is defined as the sequence of items with
index k such that i <= k < j.
          If i or j is greater than len(s), use len(s). If i is omitted, use
len(s). If i is greater than or
          equal to j, the slice is empty.

Operations on mutable (=modifiable) sequences (lists)

                 Operations on mutable sequences
   Operation                      Result                   Notes
s[i] =x          item i of s is replaced by x
s[i:j] = t       slice of s from i to j is replaced by t
del s[i:j]       same as s[i:j] = []
s.append(x)      same as s[len(s) : len(s)] = [x]
s.count(x)       return number of i's for which s[i] == x
s.extend(x)      same as s[len(s):len(s)]= x
s.index(x)       return smallest i such that s[i] == x      (1)
s.insert(i, x)   same as s[i:i] = [x] if i >= 0
s.pop([i])       same as x = s[i]; del s[i]; return x       (4)
s.remove(x)      same as del s[s.index(x)]                  (1)
s.reverse()      reverse the items of s in place            (3)
s.sort([cmpFct]) sort the items of s in place             (2), (3)

Notes :
    (1) raise a ValueError exception when x is not found in s (i.e. out of
range).
     (2) The sort() method takes an optional argument specifying a comparison
fct of 2 arguments (list items) which should
          return -1, 0, or 1 depending on whether the 1st argument is
considered smaller than, equal to, or larger than the 2nd
          argument. Note that this slows the sorting process down considerably.
     (3) The sort() and reverse() methods modify the list in place for economy
of space when sorting or reversing a large list.
           They don't return the sorted or reversed list to remind you of this
side effect.
     (4) [New 1.5.2] The optional  argument i defaults to -1, so that by default the last
item is removed and returned.



Operations on mappings (dictionaries)

                         Operations on mappings
        Operation                          Result                  Notes
len(d)                     the number of items in d
d[k]                       the item of d with key k                 (1)
d[k] = x                   set d[k] to x
del d[k]                   remove d[k] from d                       (1)
d.clear()                  remove all items from d
d.copy()                   a shallow copy of d
d.get(k,defaultval)        the item of d with key k                 (4)
d.has_key(k)               True if d has key k, else False
d.items()                  a copy of d's list of (key, item) pairs  (2)
d.iteritems()              an iterator over (key, value) pairs      (7)
d.iterkeys()               an iterator over the keys of d           (7)
d.itervalues()             an iterator over the values of d         (7)
d.keys()                   a copy of d's list of keys               (2)
d1.update(d2)              for k, v in d2.items(): d1[k] = v        (3)
d.values()                 a copy of d's list of values             (2)
d.pop(k)                   remove d[k] and return its value
d.popitem()                remove and return an arbitrary           (6)
                           (key, item) pair
d.setdefault(k,defaultval) the item of d with key k                 (5)

    Notes :
      TypeError is raised if key is not acceptable
      (1) KeyError is raised if key k is not in the map
      (2) Keys and values are listed in random order
      (3) d2 must be of the same type as d1
      (4) Never raises an exception if k is not in the map, instead it returns
    defaultVal.
          defaultVal is optional, when not provided and k is not in the map,
    None is returned.
      (5) Never raises an exception if k is not in the map, instead it returns
    defaultVal, and adds k to map with value defaultVal. defaultVal is
    optional. When not provided and k is not in the map, None is returned and
    added to map.
      (6) Raises a KeyError if the dictionary is emtpy.
      (7) While iterating over a dictionary, the values may be updated but
          the keys cannot be changed.

Operations on strings

Note that these string methods largely (but not completely) supersede the
functions available in the string module.


                             Operations on strings
    Operation                             Result                          Notes
s.capitalize()    return a copy of s with only its first character
                  capitalized.
s.center(width)   return a copy of s centered in a string of length width  (1)
                  .
s.count(sub[      return the number of occurrences of substring sub in     (2)
,start[,end]])    string s.
s.decode(([       return a decoded version of s.                           (3)
  encoding
  [,errors]])
s.encode([        return an encoded version of s. Default encoding is the
  encoding        current default string encoding.                         (3)
  [,errors]])
s.endswith(suffix return true if s ends with the specified suffix,         (2)
  [,start[,end]]) otherwise return False.
s.expandtabs([    return a copy of s where all tab characters are          (4)
tabsize])         expanded using spaces.
s.find(sub[,start return the lowest index in s where substring sub is      (2)
[,end]])          found. Return -1 if sub is not found.
s.index(sub[      like find(), but raise ValueError when the substring is  (2)
,start[,end]])    not found.
s.isalnum()       return True if all characters in s are alphanumeric,     (5)
                  False otherwise.
s.isalpha()       return True if all characters in s are alphabetic,       (5)
                  False otherwise.
s.isdigit()       return True if all characters in s are digit             (5)
                  characters, False otherwise.
s.islower()       return True if all characters in s are lowercase, False  (6)
                  otherwise.
s.isspace()       return True if all characters in s are whitespace        (5)
                  characters, False otherwise.
s.istitle()       return True if string s is a titlecased string, False    (7)
                  otherwise.
s.isupper()       return True if all characters in s are uppercase, False  (6)
                  otherwise.
s.join(seq)       return a concatenation of the strings in the sequence
                  seq, separated by 's's.
s.ljust(width)    return s left justified in a string of length width.    (1),
                                                                           (8)
s.lower()         return a copy of s converted to lowercase.
s.lstrip()        return a copy of s with leading whitespace removed.
s.replace(old,    return a copy of s with all occurrences of substring     (9)
new[, maxsplit])  old replaced by new.
s.rfind(sub[      return the highest index in s where substring sub is     (2)
,start[,end]])    found. Return -1 if sub is not found.
s.rindex(sub[     like rfind(), but raise ValueError when the substring    (2)
,start[,end]])    is not found.
s.rjust(width)    return s right justified in a string of length width.   (1),
                                                                           (8)
s.rstrip()        return a copy of s with trailing whitespace removed.
s.split([sep[     return a list of the words in s, using sep as the       (10)
,maxsplit]])      delimiter string.
s.splitlines([    return a list of the lines in s, breaking at line       (11)
keepends])        boundaries.
s.startswith      return true if s starts with the specified prefix,
(prefix[,start[   otherwise return false.                                  (2)
,end]])
s.strip()         return a copy of s with leading and trailing whitespace
                  removed.
s.swapcase()      return a copy of s with uppercase characters converted
                  to lowercase and vice versa.
                  return a titlecased copy of s, i.e. words start with
s.title()         uppercase characters, all remaining cased characters
                  are lowercase.
s.translate(table return a copy of s mapped through translation table     (12)
[,deletechars])   table.
s.upper()         return a copy of s converted to uppercase.
s.zfill(width)    return a string padded with zeroes on the left side and
                  sliding a minus sign left if necessary.  never truncates.

Notes :
    (1) Padding is done using spaces.
    (2) If optional argument start is supplied, substring s[start:] is
processed. If optional arguments start and end are supplied, substring s[start:
end] is processed.
    (3) Optional argument errors may be given to set a different error handling
scheme. The default for errors is 'strict', meaning that encoding errors raise
a ValueError. Other possible values are 'ignore' and 'replace'.
    (4) If optional argument tabsize is not given, a tab size of 8 characters
is assumed.
    (5) Returns false if string s does not contain at least one character.
    (6) Returns false if string s does not contain at least one cased
character.
    (7) A titlecased string is a string in which uppercase characters may only
follow uncased characters and lowercase characters only cased ones.
    (8) s is returned if width is less than len(s).
    (9) If the optional argument maxsplit is given, only the first maxsplit
occurrences are replaced.
    (10) If sep is not specified or None, any whitespace string is a separator.
If maxsplit is given, at most maxsplit splits are done.
    (11) Line breaks are not included in the resulting list unless keepends is
given and true.
    (12) table must be a string of length 256. All characters occurring in the
optional argument deletechars are removed prior to translation.

String formatting with the % operator

formatString % args--> evaluates to a string

  * formatString uses C printf format codes : %, c, s, i, d, u, o, x, X, e, E,
    f, g, G, r (details below).
  * Width and precision may be a * to specify that an integer argument gives
    the actual width or precision.
  * The flag characters -, +, blank, # and 0 are understood. (details below)
  * %s will convert any type argument to string (uses str() function)
  * args may be a single arg or a tuple of args

        '%s has %03d quote types.' % ('Python', 2)  # => 'Python has 002 quote types.'

  * Right-hand-side can also be a mapping:

        a = '%(lang)s has %(c)03d quote types.' % {'c':2, 'lang':'Python}
(vars() function very handy to use on right-hand-side.)

                                 Format codes
Conversion                               Meaning
d          Signed integer decimal.
i          Signed integer decimal.
o          Unsigned octal.
u          Unsigned decimal.
x          Unsigned hexadecimal (lowercase).
X          Unsigned hexadecimal (uppercase).
e          Floating point exponential format (lowercase).
E          Floating point exponential format (uppercase).
f          Floating point decimal format.
F          Floating point decimal format.
g          Same as "e" if exponent is greater than -4 or less than precision,
           "f" otherwise.
G          Same as "E" if exponent is greater than -4 or less than precision,
           "F" otherwise.
c          Single character (accepts integer or single character string).
r          String (converts any python object using repr()).
s          String (converts any python object using str()).
%          No argument is converted, results in a "%" character in the result.
           (The complete specification is %%.)

                          Conversion flag characters
Flag                                  Meaning
#    The value conversion will use the ``alternate form''.
0    The conversion will be zero padded.
-    The converted value is left adjusted (overrides "-").
     (a space) A blank should be left before a positive number (or empty
     string) produced by a signed conversion.
+    A sign character ("+" or "-") will precede the conversion (overrides a
     "space" flag).

File Objects

Created with built-in function open; may be created by other modules' functions
as well.

Operators on file objects

                                File operations
    Operation                                Result
f.close()         Close file f.
f.fileno()        Get fileno (fd) for file f.
f.flush()         Flush file f's internal buffer.
f.isatty()        True if file f is connected to a tty-like dev, else False.
f.read([size])    Read at most size bytes from file f and return as a string
                  object. If size omitted, read to EOF.
f.readline()      Read one entire line from file f.
f.readlines()     Read until EOF with readline() and return list of lines read.
                  Set file f's position, like "stdio's fseek()".
f.seek(offset[,   whence == 0 then use absolute indexing.
whence=0])        whence == 1 then offset relative to current pos.
                  whence == 2 then offset relative to file end.
f.tell()          Return file f's current position (byte offset).
f.write(str)      Write string to file f.
f.writelines(list Write list of strings to file f.
)

File Exceptions

  EOFError
     End-of-file hit when reading (may be raised many times, e.g. if f is a
    tty).
  IOError
     Other I/O-related I/O operation failure.
  OSError
     OS system call failed.


    Advanced Types

    -See manuals for more details -
      + Module objects
      + Class objects
      + Class instance objects
      + Type objects (see module: types)
      + File objects (see above)
      + Slice objects
      + XRange objects
      + Callable types:
          o User-defined (written in Python):
              # User-defined Function objects
              # User-defined Method objects
          o Built-in (written in C):
              # Built-in Function objects
              # Built-in Method objects
      + Internal Types:
          o Code objects (byte-compile executable Python code: bytecode)
          o Frame objects (execution frames)
          o Traceback objects (stack trace of an exception)


    Statements

    pass            -- Null statement
    del name[,name]* -- Unbind name(s) from object. Object will be indirectly
                        (and automatically) deleted only if no longer referenced.
    print [>> fileobject,] [s1 [, s2 ]* [,]
                    -- Writes to sys.stdout, or to fileobject if supplied.
                       Puts spaces between arguments. Puts newline at end
                       unless statement ends with comma.
                       Print is not required when running interactively,
                       simply typing an expression will print its value,
                       unless the value is None.
    exec x [in globals [,locals]]
                    -- Executes x in namespaces provided. Defaults
                       to current namespaces. x can be a string, file
                       object or a function object.
    callable(value,... [id=value], [*args], [**kw])
                    -- Call function callable with parameters. Parameters can
                       be passed by name or be omitted if function
                       defines default values. E.g. if callable is defined as
                       "def callable(p1=1, p2=2)"
                       "callable()"       <=>  "callable(1, 2)"
                       "callable(10)"     <=>  "callable(10, 2)"
                       "callable(p2=99)"  <=>  "callable(1, 99)"
                       *args is a tuple of positional arguments.
                       **kw is a dictionary of keyword arguments.

    Assignment operators

                              Caption
    Operator                    Result                     Notes
    a = b    Basic assignment - assign object b to label a  (1)
    a += b   Roughly equivalent to a = a + b                (2)
    a -= b   Roughly equivalent to a = a - b                (2)
    a *= b   Roughly equivalent to a = a * b                (2)
    a /= b   Roughly equivalent to a = a / b                (2)
    a %= b   Roughly equivalent to a = a % b                (2)
    a **= b  Roughly equivalent to a = a ** b               (2)
    a &= b   Roughly equivalent to a = a & b                (2)
    a |= b   Roughly equivalent to a = a | b                (2)
    a ^= b   Roughly equivalent to a = a ^ b                (2)
    a >>= b  Roughly equivalent to a = a >> b               (2)
    a <<= b  Roughly equivalent to a = a << b               (2)

    Notes :
        (1) Can unpack tuples, lists, and strings.
           first, second = a[0:2]; [f, s] = range(2); c1,c2,c3='abc'
           Tip: x,y = y,x swaps x and y.
        (2) Not exactly equivalent - a is evaluated only once. Also, where
    possible, operation performed in-place - a is modified rather than
    replaced.

    Control Flow

    if condition: suite
    [elif condition: suite]*
    [else: suite]   -- usual if/else_if/else statement
    while condition: suite
    [else: suite]
                    -- usual while statement. "else" suite is executed
                       after loop exits, unless the loop is exited with
                       "break"
    for element in sequence: suite
    [else: suite]
                    -- iterates over sequence, assigning each element to element.
                       Use built-in range function to iterate a number of times.
                       "else" suite executed at end unless loop exited
                       with "break"
    break           -- immediately exits "for" or "while" loop
    continue        -- immediately does next iteration of "for" or "while" loop
    return [result] -- Exits from function (or method) and returns result (use a tuple to
                       return more than one value). If no result given, then returns None.
    yield result    -- Freezes the execution frame of a generator and returns the result
                       to the iterator's .next() method.  Upon the next call to next(),
                       resumes execution at the frozen point with all of the local variables
                       still intact.

    Exception Statements

    assert expr[, message]
                    -- expr is evaluated. if false, raises exception AssertionError
                       with message. Inhibited if __debug__ is 0.
    try: suite1
    [except [exception [, value]: suite2]+
    [else: suite3]
                    -- statements in suite1 are executed. If an exception occurs, look
                       in "except" clauses for matching <exception>. If matches or bare
                       "except" execute suite of that clause. If no exception happens
                       suite in "else" clause is executed after suite1.
                       If exception has a value, it is put in value.
                       exception can also be tuple of exceptions, e.g.
                       "except (KeyError, NameError), val: print val"
    try: suite1
    finally: suite2
                    -- statements in suite1 are executed. If no
                       exception, execute suite2 (even if suite1 is
                       exited with a "return", "break" or "continue"
                       statement). If exception did occur, executes
                       suite2 and then immediately reraises exception.
    raise exception [,value [, traceback]]
                    -- raises exception with optional value
                       value. Arg traceback specifies a traceback object to
                       use when printing the exception's backtrace.
    raise           -- a raise statement without arguments re-raises
                       the last exception raised in the current function
An exception is either a string (object) or a class instance.
  Can create a new one simply by creating a new string:

              my_exception = 'You did something wrong'
      try:
                   if bad:
              raise my_exception, bad
      except my_exception, value:
                    print 'Oops', value

Exception classes must be derived from the predefined class: Exception, e.g.:
            class text_exception(Exception): pass
            try:
                if bad:
                    raise text_exception()
                    # This is a shorthand for the form
                    # "raise <class>, <instance>"
             except Exception:
                 print 'Oops'
                 # This will be printed because
                 # text_exception is a subclass of Exception
When an error message is printed for an unhandled exception which is a
class, the class name is printed, then a colon and a space, and
finally the instance converted to a string using the built-in function
str().
All built-in exception classes derives from StandardError, itself
derived from Exception.

Name Space Statements

[1.51: On Mac & Windows, the case of module file names must now match the case
as used
  in the import statement]
Packages (>1.5): a package is a name space which maps to a directory including
                module(s) and the special initialization module '__init__.py'
                (possibly empty). Packages/dirs can be nested. You address a
                module's symbol via '[package.[package...]module.symbol's.
import module1 [as name1] [, module2]*
                -- imports modules. Members of module must be
                   referred to by qualifying with [package.]module name:
                   "import sys; print sys.argv:"
                   "import package1.subpackage.module; package1.subpackage.module.foo()"
                   module1 renamed as name1, if supplied.
from module import name1 [as othername1] [, name2]*
                -- imports names from module module in current namespace.
                   "from sys import argv; print argv"
                   "from package1 import module; module.foo()"
                   "from package1.module import foo; foo()"
                   name1 renamed as othername1, if supplied.
from module import *
                -- imports all names in module, except those starting with "_";
                   *to be used sparsely, beware of name clashes* :
                   "from sys import *; print argv"
                   "from package.module import *; print x'
                    NB: "from package import *" only imports the symbols defined
                    in the package's __init__.py file, not those in the
                    template modules!
global name1 [, name2]*
                -- names are from global scope (usually meaning from module)
                   rather than local (usually meaning only in function).
                -- E.g. in fct without "global" statements, assuming
                   "a" is name that hasn't been used in fct or module
                   so far:
                   -Try to read from "a" -> NameError
                   -Try to write to "a" -> creates "a" local to fcn
                   -If "a" not defined in fct, but is in module, then
                       -Try to read from "a", gets value from module
                       -Try to write to "a", creates "a" local to fct
                   But note "a[0]=3" starts with search for "a",
                   will use to global "a" if no local "a".

Function Definition

def func_id ([param_list]): suite
                -- Creates a function object & binds it to name func_id.

    param_list ::= [id [, id]*]
    id ::= value | id = value | *id | **id
    [Args are passed by value.Thus only args representing a mutable object
    can be modified (are inout parameters). Use a tuple to return more than
    one value]

Example:
        def test (p1, p2 = 1+1, *rest, **keywords):
            -- Parameters with "=" have default value (v is
               evaluated when function defined).
               If list has "*id" then id is assigned a tuple of
               all remaining args passed to function (like C vararg)
               If list has "**id" then id is assigned a dictionary of
               all extra arguments passed as keywords.

Class Definition

class <class_id> [(<super_class1> [,<super_class2>]*)]: <suite>
        -- Creates a class object and assigns it name <class_id>
           <suite> may contain local "defs" of class methods and
           assignments to class attributes.
Example:
       class my_class (class1, class_list[3]): ...
                  Creates a class object inheriting from both "class1" and whatever
                  class object "class_list[3]" evaluates to. Assigns new
                  class object to name "my_class".
        - First arg to class methods is always instance object, called 'self'
          by convention.
        - Special method __init__() is called when instance is created.
        - Special method __del__() called when no more reference to object.
        - Create instance by "calling" class object, possibly with arg
          (thus instance=apply(aClassObject, args...) creates an instance!)
        - In current implementation, can't subclass off built-in
          classes. But can "wrap" them, see UserDict & UserList modules,
          and see __getattr__() below.
Example:
        class c (c_parent):
           def __init__(self, name): self.name = name
           def print_name(self): print "I'm", self.name
           def call_parent(self): c_parent.print_name(self)
           instance = c('tom')
           print instance.name
           'tom'
           instance.print_name()
           "I'm tom"
        Call parent's super class by accessing parent's method
        directly and passing "self" explicitly (see "call_parent"
        in example above).
        Many other special methods available for implementing
        arithmetic operators, sequence, mapping indexing, etc.

Documentation Strings

Modules, classes and functions may be documented by placing a string literal by
itself as the first statement in the suite. The documentation can be retrieved
by getting the '__doc__' attribute from the module, class or function.
Example:
        class C:
            "A description of C"
            def __init__(self):
                "A description of the constructor"
                # etc.
Then c.__doc__ == "A description of C".
Then c.__init__.__doc__ == "A description of the constructor".

Others

lambda [param_list]: returnedExpr
                -- Creates an anonymous function. returnedExpr must be
                   an expression, not a statement (e.g., not "if xx:...",
                   "print xxx", etc.) and thus can't contain newlines.
                   Used mostly for filter(), map(), reduce() functions, and GUI callbacks..
List comprehensions
result = [expression for item1 in sequence1  [if condition1]
                        [for item2 in sequence2 ... for itemN in sequenceN]
                      ]
is equivalent to:
result = []
for item1 in sequence1:
    for item2 in sequence2:
    ...
        for itemN in sequenceN:
             if (condition1) and furthur conditions:
                  result.append(expression)



Built-In Functions

                              Built-In Functions
     Function                                 Result
__import__(name[,   Imports module within the given context (see lib ref for
globals[, locals[,  more details)
fromlist]]])
abs(x)              Return the absolute value of number x.
apply(f, args[,     Calls func/method f with arguments args and optional
keywords])          keywords.
bool(x)             Returns True when the argument x is true and False otherwise.
buffer(obj)         Creates a buffer reference to an object.
callable(x)         Returns True if x callable, else False.
chr(i)              Returns one-character string whose ASCII code isinteger i
classmethod(f)      Converts a function f, into a method with the class as the
                    first argument.  Useful for creating alternative constructors.
cmp(x,y)            Returns negative, 0, positive if x <, ==, > to y
coerce(x,y)         Returns a tuple of the two numeric arguments converted to a
                    common type.
                    Compiles string into a code object.filename is used in
                    error message, can be any string. It isusually the file
compile(string,     from which the code was read, or eg. '<string>'if not read
filename, kind)     from file.kind can be 'eval' if string is a single stmt, or
                    'single' which prints the output of expression statements
                    thatevaluate to something else than None, or be 'exec'.
complex(real[,      Builds a complex object (can also be done using J or j
image])             suffix,e.g. 1+3J)
delattr(obj, name)  deletes attribute named name of object obj <=> del obj.name
                    If no args, returns the list of names in current
dict([items])       Create a new dictionary from the specified item list.
dir([object])       localsymbol table. With a module, class or class
                    instanceobject as arg, returns list of names in its attr.
                    dict.
divmod(a,b)         Returns tuple of (a/b, a%b)
enumerate(seq)      Return a iterator giving:  (0, seq[0]), (1, seq[1]), ...
eval(s[, globals[,  Eval string s in (optional) globals, locals contexts.s must
locals]])           have no NUL's or newlines. s can also be acode object.
                    Example: x = 1; incr_x = eval('x + 1')
execfile(file[,     Executes a file without creating a new module, unlike
globals[, locals]]) import.
file()              Synonym for open().
filter(function,    Constructs a list from those elements of sequence for which
sequence)           function returns true. function takes one parameter.
float(x)            Converts a number or a string to floating point.
getattr(object,     [<default> arg added in 1.5.2]Gets attribute called name
name[, default]))   from object,e.g. getattr(x, 'f') <=> x.f). If not found,
                    raisesAttributeError or returns default if specified.
globals()           Returns a dictionary containing current global variables.
hasattr(object,     Returns true if object has attr called name.
name)
hash(object)        Returns the hash value of the object (if it has one)
help(f)             Display documentation on object f.
hex(x)              Converts a number x to a hexadecimal string.
id(object)          Returns a unique 'identity' integer for an object.
input([prompt])     Prints prompt if given. Reads input and evaluates it.
                    Converts a number or a string to a plain integer. Optional
int(x[, base])      base paramenter specifies base from which to convert string
                    values.
intern(aString)     Enters aString in the table of "interned strings"
                    andreturns the string. Interned strings are 'immortals'.
isinstance(obj,     returns true if obj is an instance of class. Ifissubclass
class)              (A,B) then isinstance(x,A) => isinstance(x,B)
issubclass(class1,  returns true if class1 is derived from class2
class2)
                    Returns the length (the number of items) of an object
iter(collection)    Returns an iterator over the collection.
len(obj)            (sequence, dictionary, or instance of class implementing
                    __len__).
list(sequence)      Converts sequence into a list. If already a list,returns a
                    copy of it.
locals()            Returns a dictionary containing current local variables.
                    Converts a number or a string to a long integer. Optional
long(x[, base])     base paramenter specifies base from which to convert string
                    values.
                    Applies function to every item of list and returns a listof
map(function, list, the results. If additional arguments are passed,function
...)                must take that many arguments and it is givento function on
                    each call.
max(seq)            Returns the largest item of the non-empty sequence seq.
min(seq)            Returns the smallest item of a non-empty sequence seq.
oct(x)              Converts a number to an octal string.
open(filename [,    Returns a new file object. First two args are same asthose
mode='r', [bufsize= for C's "stdio open" function. bufsize is 0for unbuffered,
implementation      1 for line-buffered, negative forsys-default, all else, of
dependent]])        (about) given size.
ord(c)              Returns integer ASCII value of c (a string of len 1). Works
                    with Unicode char.
object()            Create a base type.  Used as a superclass for new-style objects.
open(name           Open a file.
  [, mode
  [, buffering]])
pow(x, y [, z])     Returns x to power y [modulo z]. See also ** operator.
property()          Created a property with access controlled by functions.
range(start [,end   Returns list of ints from >= start and < end.With 1 arg,
[, step]])          list from 0..arg-1With 2 args, list from start..end-1With 3
                    args, list from start up to end by step
raw_input([prompt]) Prints prompt if given, then reads string from stdinput (no
                    trailing \n). See also input().
reduce(f, list [,   Applies the binary function f to the items oflist so as to
init])              reduce the list to a single value.If init given, it is
                    "prepended" to list.
                    Re-parses and re-initializes an already imported module.
                    Useful in interactive mode, if you want to reload amodule
reload(module)      after fixing it. If module was syntacticallycorrect but had
                    an error in initialization, mustimport it one more time
                    before calling reload().
                    Returns a string containing a printable and if possible
repr(object)        evaluable representation of an object. <=> `object`
                    (usingbackquotes). Class redefinissable (__repr__). See
                    also str()
round(x, n=0)       Returns the floating point value x rounded to n digitsafter
                    the decimal point.
setattr(object,     This is the counterpart of getattr().setattr(o, 'foobar',
name, value)        3) <=> o.foobar = 3Creates attribute if it doesn't exist!
slice([start,] stop Returns a slice object representing a range, with R/
[, step])           Oattributes: start, stop, step.
                    Returns a string containing a nicely
staticmethod()      Convert a function to method with no self or class
                    argument.  Useful for methods associated with a class that
                    do not need access to an object's internal state.
str(object)         printablerepresentation of an object. Class overridable
                    (__str__).See also repr().
super(type)         Create an unbound super object.  Used to call cooperative
                    superclass methods.
sum(sequence,       Add the values in the sequence and return the sum.
    [start])
tuple(sequence)     Creates a tuple with same elements as sequence. If already
                    a tuple, return itself (not a copy).
                    Returns a type object [see module types] representing
                    thetype of obj. Example: import typesif type(x) ==
type(obj)           types.StringType: print 'It is a string'NB: it is
                    recommanded to use the following form:if isinstance(x,
                    types.StringType): etc...
unichr(code)        code.
unicode(string[,    Creates a Unicode string from a 8-bit string, using
encoding[, error    thegiven encoding name and error treatment (…