Python 2.6 Quick Reference (Letter) (2009).pdf

Python 2.6 Quick Reference

Contents

Front matter

Invocation Options

Environment variables

Lexical entities : keywords , identifiers , string literals , boolean constants , numbers , sequences , dictionaries ,

operators

Basic types and their operations: None , bool , Numeric types , sequence types , list , dictionary , string , file , set ,

named tuples , date/time

Advanced types

Statements : assignment , conditional expressions , control flow , exceptions , name space , function def , class def

Iterators ; Generators ; Descriptors ; Decorators

Built-in Functions

Built-in Exceptions

Standard methods & operators redefinition in usercreated Classes

Special informative state attributes for some types

Important modules : sys , os , posix , posixpath , shutil , time , string , re , math , getopt

List of modules in the base distribution

Workspace exploration and idiom hints

Python mode for Emacs

Front matter

Version 2.6 ( What's new? )

Check updates at http://rgruet.free.fr/#QuickRef .

Please report errors, inaccuracies and suggestions to Richard Gruet (pqr at rgruet.net).

Creative Commons License.

Last updated on February 10, 2009.

Feb 10, 2008

upgraded by Richard Gruet and Josh Stone for Python 2.6

Dec 14, 2006

upgraded by Richard Gruet for Python 2.5

Feb 17, 2005,

upgraded by Richard Gruet for Python 2.4

Oct 3, 2003

upgraded by Richard Gruet for Python 2.3

May 11, 2003, rev 4

upgraded by Richard Gruet for Python 2.2 (restyled by Andrei )

Aug 7, 2001

upgraded by Simon Brunning for Python 2.1

May 16, 2001

upgraded by Richard Gruet and Simon Brunning for Python 2.0

Jun 18, 2000

upgraded by Richard Gruet for Python 1.5.2

Oct 20, 1995

created by Chris Hoffmann for Python 1.3

Color coding:

Features added in 2.6 since 2.5

Features added in 2.5 since 2.4

Features added in 2.4 since 2.3

Originally based on:

Python Bestiary, author: Ken Manheimer

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Python 2.6 Quick Reference

Python manuals , authors: Guido van Rossum and Fred Drake

pythonmode.el, author: Tim Peters

and the readers of comp.lang.python

Useful links :

Python's nest : http://www.python.org

Official documentation : http://docs.python.org/2.6/

Other doc & free books : FAQs , Faqts , Dive into Python , Python Cookbook , Thinking in Python , Text processing in

Python

Getting started : Python Tutorial , 7mn to Hello World (windows)

Topics : HOWTOs , Databases , Web programming , XML , Web Services , Parsers , Numeric & Scientific Computing , GUI

programming , Distributing

Where to find packages : Python Package Index (PyPI) , Python Eggs , SourceForge (search "python") , Easy Install ,

O'Reilly Python DevCenter

Wiki : moinmoin

Newsgroups : comp.lang.python and comp.lang.python.announce

Misc pages : Daily Python URL

Python Development : http://www.python.org/dev/

Jython Java implementation of Python: http://www.jython.org/

IronPython Python on .Net: http://www.codeplex.com/Wiki/View.aspx?ProjectName=IronPython

ActivePython : http://www.ActiveState.com/ASPN/Python/

Help desk : help@python.org

2 excellent (but somehow outdated) Python reference books : Python Essential Reference (Python 2.1) by David

Beazley & Guido Van Rossum (Other New Riders) and Python in a nutshell by Alex martelli (O'Reilly).

Python 2.4 Reference Card (cheatsheet) by Laurent Pointal, designed for printing (15 pages).

Online Python 2.2 Quick Reference by the New Mexico Tech Computer Center.

Tip : From within the Python interpreter, type help , help( object ) or help(" name ") to get help.

Invocation Options

python [ w ] [BdEhimOQsStuUvVWxX3?] [c command | scriptFile | ] [ args ]

(python w does not open a terminal/console; python does)

Invocation Options

Option Effect

B Prevents module imports from creating .pyc or .pyo files (see also envt variable

PYTHONDONTWRITEBYTECODE=x and attribute sys.dont_write_bytecode ).

d Output parser debugging information (also PYTHONDEBUG=x)

E Ignore environment variables (such as PYTHONPATH)

h Print a help message and exit (formerly ?)

i Inspect interactively after running script (also PYTHONINSPECT=x) and force prompts, even if stdin

appears not to be a terminal.

m module Search for module on sys.path and runs the module as a script. (Implementation improved in 2.5:

module runpy )

O Optimize generated bytecode (also PYTHONOPTIMIZE=x). Asserts are suppressed.

OO Remove docstrings in addition to the O optimizations.

Q arg Division options: Qold (default), Qwarn, Qwarnall, Qnew

s Disables the userspecific module path (also PYTHONNOUSERSITE=x)

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).

U Force Python to interpret all string literals as Unicode literals.

v Verbose (trace import statements) (also PYTHONVERBOSE=x).

V Print the Python version number and exit.

W arg Warning control (arg is action:message:category:module:lineno)

Skip first line of source, allowing use of nonunix Forms of #!cmd

Disable class based builtin exceptions (for backward compatibility management of exceptions)

Emit a DeprecationWarning for Python 3.x incompatibilities

Specify the command to execute (see next section). This terminates the option list (following

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Python 2.6 Quick Reference

command options are passed as arguments to the command).

scriptFile The name of a python file (.py) to execute. Read from stdin.

Program read from stdin (default; interactive mode if a tty).

args

Passed to script or command (in sys.argv[1:] )

If no scriptFile or command, Python enters interactive mode.

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

IPython (enhanced interactive Python shell), Eric , SPE , BOA constructor , PyDev (Eclipse plugin).

Typical python module header :

#!/usr/bin/env python

# -*- coding: latin1 -*-

Since 2.3 the encoding of a Python source file must be declared as one of the two first lines (or defaults to 7

bits Ascii ) [ PEP0263 ], with the format:

# -*- coding: encoding -*-

Std encodings are defined here , e.g. ISO88591 (aka latin1), iso885915 (latin9), UTF8... Not all encodings

supported, in particular UTF16 is not supported.

It's now a syntax error if a module contains string literals with 8bit characters but doesn't have an encoding

declaration (was a warning before).

Since 2.5, from __future__ import feature statements must be declared at beginning of source file.

Site customization : File sitecustomize.py is automatically loaded by Python if it exists in the Python path

(ideally located in ${PYTHONHOME}/lib/site-packages/ ).

Tip: when launching a Python script on Windows,

<pythonHome>\python myScript.py args ... can be reduced to :

myScript.py args ... if <pythonHome> is in the PATH envt variable, and further reduced to :

myScript args ... provided that .py;.pyw;.pyc;.pyo is added to the PATHEXT envt variable.

Environment variables

Variable

Effect

PYTHONHOME

Alternate prefix directory (or prefix : exec_prefix ). The default module search

path uses prefix /lib

PYTHONPATH

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 !

On Windows Python first searches for Registry key

HKEY_LOCAL_MACHINE\Software\Python\PythonCore\ x.y \PythonPath (default

value). You can create a key named after your application with a default string

value giving the root directory path of your appl.

Alternatively, you can create a text file with a .pth extension, containing the

path(s), one per line, and put the file somewhere in the Python search path

(ideally in the site-packages/ directory). It's better to create a .pth for each

application, to make easy to uninstall them.

PYTHONSTARTUP If this is the name of a readable file, the Python commands in that file are

executed before the first prompt is displayed in interactive mode (no default).

PYTHONDEBUG If nonempty, same as d option

PYTHONINSPECT If nonempty, same as i option

PYTHONOPTIMIZE If nonempty, same as O option

PYTHONUNBUFFERED If nonempty, same as u option

PYTHONVERBOSE If nonempty, same as v option

PYTHONCASEOK If nonempty, ignore case in file/module names (imports)

PYTHONDONTWRITEBYTECODE If nonempty, same as B option

PYTHONIOENCODING

Alternate encodingname or encodingname:errorhandler for stdin, stdout, and

stderr, with the same choices accepted by str.encode() .

PYTHONUSERBASE

Provides a private site-packages directory for user-specific modules. [PEP

0370]

On Unix and Mac OS X, defaults to ~/.local/ , and modules are found in a

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Python 2.6 Quick Reference

versionspecific subdirectory like lib/python2.6/site-packages .

On Windows, defaults to %APPDATA%/Python and Python26/site-packages .

PYTHONNOUSERSITE

If nonempty, same as s option

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 with

def finally in print yield

(List of keywords available in std module: keyword )

Illegitimate Tokens (only valid in strings): $ ? (plus @ before 2.4)

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 triplequoted 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

(classprivate name mangling).

String literals

Two flavors: str (standard 8 bits localedependent strings, like ascii, iso 88591, utf8, ...) and unicode (16 or 32

bits/char in utf16 mode or 32 bits/char in utf32 mode); one common ancestor basestring .

Literal

" 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 """

b" An 8bit string " A bytes instance, a forwardcompatible form for an 8bit string '

B" Another 8bit string "

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

Escape

Meaning

\ newline

Ignored (escape newline)

Backslash (\)

Escape (ESC)

Vertical Tab (VT)

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Python 2.6 Quick Reference

\' Single quote (')

\f Formfeed (FF)

\ ooo char with octal value ooo

\" Double quote (")

\n Linefeed (LF)

\a Bell (BEL)

\r Carriage Return (CR)

\x hh char with hex value hh

\b Backspace (BS)

\t Horizontal Tab (TAB)

\u xxxx Character with 16bit hex value xxxx (unicode only)

\U xxxxxxxx Character with 32bit hex value xxxxxxxx (unicode only)

\N{ name } Character named in the Unicode database (unicode only), e.g. u'\N{Greek Small Letter

Pi}' <=> u'\u03c0'.

(Conversely, in module unicodedata, unicodedata.name(u'\u03c0') == 'GREEK SMALL

LETTER PI' )

\ AnyOtherChar left asis, including the backslash, e.g. str('\z') == '\\z'

NUL byte ( \000 ) is not an endofstring marker; NULs may be embedded in strings.

Strings (and tuples) are immutable : they cannot be modified.

Boolean constants (since 2.2.1)

True

False

In 2.2.1, True and False are integers 1 and 0. Since 2.3, they are of new type bool .

Numbers

Decimal integer : 1234, 1234567890546378940 L (or l )

Binary integer: 0b 10, 0B 10, 0b 10101010101010101010101010101010L (begins with a 0b or 0B )

Octal integer: 0 177, 0o 177, 0O 177, 0 177777777777777777L (begins with a 0 , 0o , or 0O )

Hex integer: 0x FF, 0X FFFFffffFFFFFFFFFFL (begins with 0x or 0X )

Long integer (unlimited precision): 1234567890123456 L (ends with L or l ) or long( 1234 )

Float (double precision): 3 . 14 e-10 , .001, 10., 1E3

Complex : 1 J , 2 + 3 J , 4 + 5 j (ends with J or j , + separates (float) real and imaginary parts)

Integers and long integers are unified starting from release 2.2 (the L suffix is no longer required)

Sequences

Strings (types str and unicode ) of length 0, 1, 2 (see above )

'', '1', "12", 'hello\n'

Tuples (type tuple ) of length 0, 1, 2, etc:

() (1 , ) (1,2) # parentheses are optional if len > 0

Lists (type 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 [ : step] ] . Start defaults to 0, end to len(sequence),

step to 1.

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.

a[::2] == (0, 2, 4, 6) # Only even numbers.

a[::-1] = (7, 6, 5, 4, 3 , 2, 1, 0) # Reverse order.

Dictionaries (Mappings)

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