PYTHON(1) PYTHON(1)
NAME
python - an interpreted, interactive, object-oriented programming language
SYNOPSIS
python [ -d ] [ -E ] [ -h ] [ -i ] [ -m module-name ] [ -O ]
[ -Q argument ] [ -S ] [ -t ] [ -u ]
[ -v ] [ -V ] [ -W argument ] [ -x ]
[ -c command | script | - ] [ arguments ]
DESCRIPTION
Python is an interpreted, interactive, object-oriented programming language that combines remarkable
power with very clear syntax. For an introduction to programming in Python you are referred to the
Python Tutorial. The Python Library Reference documents built-in and standard types, constants,
functions and modules. Finally, the Python Reference Manual describes the syntax and semantics of
the core language in (perhaps too) much detail. (These documents may be located via the INTERNET
RESOURCES below; they may be installed on your system as well.)
Python's basic power can be extended with your own modules written in C or C++. On most systems such
modules may be dynamically loaded. Python is also adaptable as an extension language for existing
applications. See the internal documentation for hints.
Documentation for installed Python modules and packages can be viewed by running the pydoc program.
COMMAND LINE OPTIONS
-c command
Specify the command to execute (see next section). This terminates the option list (following
options are passed as arguments to the command).
-d Turn on parser debugging output (for wizards only, depending on compilation options).
-E Ignore environment variables like PYTHONPATH and PYTHONHOME that modify the behavior of the
interpreter.
-h Prints the usage for the interpreter executable and exits.
-i When a script is passed as first argument or the -c option is used, enter interactive mode
after executing the script or the command. It does not read the $PYTHONSTARTUP file. This
can be useful to inspect global variables or a stack trace when a script raises an exception.
-m module-name
Searches sys.path for the named module and runs the corresponding .py file as a script.
-O Turn on basic optimizations. This changes the filename extension for compiled (bytecode)
files from .pyc to .pyo. Given twice, causes docstrings to be discarded.
-Q argument
Division control; see PEP 238. The argument must be one of "old" (the default, int/int and
long/long return an int or long), "new" (new division semantics, i.e. int/int and long/long
returns a float), "warn" (old division semantics with a warning for int/int and long/long), or
"warnall" (old division semantics with a warning for all use of the division operator). For a
use of "warnall", see the Tools/scripts/fixdiv.py script.
-S Disable the import of the module site and the site-dependent manipulations of sys.path that it
entails.
-t Issue a warning when a source file mixes tabs and spaces for indentation in a way that makes
it depend on the worth of a tab expressed in spaces. Issue an error when the option is given
twice.
-u Force stdin, stdout and stderr to be totally unbuffered. On systems where it matters, also
put stdin, stdout and stderr in binary mode. Note that there is internal buffering in xread-lines(), xreadlines(),
lines(), readlines() and file-object iterators ("for line in sys.stdin") which is not influ-enced influenced
enced by this option. To work around this, you will want to use "sys.stdin.readline()" inside
a "while 1:" loop.
-v Print a message each time a module is initialized, showing the place (filename or built-in
module) from which it is loaded. When given twice, print a message for each file that is
checked for when searching for a module. Also provides information on module cleanup at exit.
-V Prints the Python version number of the executable and exits.
-W argument
Warning control. Python sometimes prints warning message to sys.stderr. A typical warning
message has the following form: file:line: category: message. By default, each warning is
printed once for each source line where it occurs. This option controls how often warnings
are printed. Multiple -W options may be given; when a warning matches more than one option,
the action for the last matching option is performed. Invalid -W options are ignored (a warn-ing warning
ing message is printed about invalid options when the first warning is issued). Warnings can
also be controlled from within a Python program using the warnings module.
The simplest form of argument is one of the following action strings (or a unique abbrevia-tion): abbreviation):
tion): ignore to ignore all warnings; default to explicitly request the default behavior
(printing each warning once per source line); all to print a warning each time it occurs (this
may generate many messages if a warning is triggered repeatedly for the same source line, such
as inside a loop); module to print each warning only only the first time it occurs in each
module; once to print each warning only the first time it occurs in the program; or error to
raise an exception instead of printing a warning message.
The full form of argument is action:message:category:module:line. Here, action is as
explained above but only applies to messages that match the remaining fields. Empty fields
match all values; trailing empty fields may be omitted. The message field matches the start
of the warning message printed; this match is case-insensitive. The category field matches
the warning category. This must be a class name; the match test whether the actual warning
category of the message is a subclass of the specified warning category. The full class name
must be given. The module field matches the (fully-qualified) module name; this match is
case-sensitive. The line field matches the line number, where zero matches all line numbers
and is thus equivalent to an omitted line number.
-x Skip the first line of the source. This is intended for a DOS specific hack only. Warning:
the line numbers in error messages will be off by one!
INTERPRETER INTERFACE
The interpreter interface resembles that of the UNIX shell: when called with standard input connected
to a tty device, it prompts for commands and executes them until an EOF is read; when called with a
file name argument or with a file as standard input, it reads and executes a script from that file;
when called with -c command, it executes the Python statement(s) given as command. Here command may
contain multiple statements separated by newlines. Leading whitespace is significant in Python
statements! In non-interactive mode, the entire input is parsed before it is executed.
If available, the script name and additional arguments thereafter are passed to the script in the
Python variable sys.argv , which is a list of strings (you must first import sys to be able to access
it). If no script name is given, sys.argv[0] is an empty string; if -c is used, sys.argv[0] contains
the string '-c'. Note that options interpreted by the Python interpreter itself are not placed in
sys.argv.
In interactive mode, the primary prompt is `>>>'; the second prompt (which appears when a command is
not complete) is `...'. The prompts can be changed by assignment to sys.ps1 or sys.ps2. The inter-preter interpreter
preter quits when it reads an EOF at a prompt. When an unhandled exception occurs, a stack trace is
printed and control returns to the primary prompt; in non-interactive mode, the interpreter exits
after printing the stack trace. The interrupt signal raises the KeyboardInterrupt exception; other
UNIX signals are not caught (except that SIGPIPE is sometimes ignored, in favor of the IOError excep-tion). exception).
tion). Error messages are written to stderr.
FILES AND DIRECTORIES
These are subject to difference depending on local installation conventions; ${prefix} and
${exec_prefix} are installation-dependent and should be interpreted as for GNU software; they may be
the same. The default for both is /usr/local.
${exec_prefix}/bin/python
Recommended location of the interpreter.
${prefix}/lib/python<version>
${exec_prefix}/lib/python<version>
Recommended locations of the directories containing the standard modules.
${prefix}/include/python<version>
${exec_prefix}/include/python<version>
Recommended locations of the directories containing the include files needed for developing
Python extensions and embedding the interpreter.
~/.pythonrc.py
User-specific initialization file loaded by the user module; not used by default or by most
applications.
ENVIRONMENT VARIABLES
PYTHONHOME
Change the location of the standard Python libraries. By default, the libraries are searched
in ${prefix}/lib/python<version> and ${exec_prefix}/lib/python<version>, where ${prefix} and
${exec_prefix} are installation-dependent directories, both defaulting to /usr/local. When
$PYTHONHOME is set to a single directory, its value replaces both ${prefix} and ${exec_pre-fix}. ${exec_prefix}.
fix}. To specify different values for these, set $PYTHONHOME to ${prefix}:${exec_prefix}.
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 colons. Non-existent directories are
silently ignored. The default search path is installation dependent, but generally begins
with ${prefix}/lib/python<version> (see PYTHONHOME above). The default search path is always
appended to $PYTHONPATH. If a script argument is given, the directory containing the script
is inserted in the path in front of $PYTHONPATH. The search path can be manipulated from
within a Python program as the variable sys.path .
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. The file is executed in the same name
space where interactive commands are executed so that objects defined or imported in it can be
used without qualification in the interactive session. You can also change the prompts
sys.ps1 and sys.ps2 in this file.
PYTHONY2K
Set this to a non-empty string to cause the time module to require dates specified as strings
to include 4-digit years, otherwise 2-digit years are converted based on rules described in
the time module documentation.
PYTHONOPTIMIZE
If this is set to a non-empty string it is equivalent to specifying the -O option. If set to
an integer, it is equivalent to specifying -O multiple times.
PYTHONDEBUG
If this is set to a non-empty string it is equivalent to specifying the -d option. If set to
an integer, it is equivalent to specifying -d multiple times.
PYTHONINSPECT
If this is set to a non-empty string it is equivalent to specifying the -i option.
PYTHONUNBUFFERED
If this is set to a non-empty string it is equivalent to specifying the -u option.
PYTHONVERBOSE
If this is set to a non-empty string it is equivalent to specifying the -v option. If set to
an integer, it is equivalent to specifying -v multiple times.
INTERACTIVE INPUT EDITING AND HISTORY SUBSTITUTION
The Python inteterpreter supports editing of the current input line and history substitution, similar
to facilities found in the Korn shell and the GNU Bash shell. However, rather than being implemented
using the GNU Readline library, this Python interpreter uses the BSD EditLine library editline(3)
with a GNU Readline emulation layer.
The readline module provides the access to the EditLine library, but there are a few major differ-ences differences
ences compared to a traditional implementation using the Readline library. The command language used
in the preference files is that of EditLine, as described in editrc(5) and not that used by the Read-line Readline
line library. This also means that the parse_and_bind() routines uses EditLine commands. And the
preference file itself is ~/.editrc instead of ~/.inputrc.
For example, the rlcompleter module, which defines a completion function for the readline modules,
works correctly with the EditLine libraries, but needs to be initialized somewhat differently:
import rlcompleter
import readline
readline.parse_and_bind("bind ^I rl_complete")
For vi mode, one needs:
readline.parse_and_bind("bind -v")
AUTHOR
The Python Software Foundation: http://www.python.org/psf
INTERNET RESOURCES
Main website: http://www.python.org/
Documentation: http://docs.python.org/
Community website: http://starship.python.net/
Developer resources: http://www.python.org/dev/
FTP: ftp://ftp.python.org/pub/python/
Module repository: http://www.vex.net/parnassus/
Newsgroups: comp.lang.python, comp.lang.python.announce
LICENSING
Python is distributed under an Open Source license. See the file "LICENSE" in the Python source dis-
tribution for information on terms & conditions for accessing and otherwise using Python and for a
DISCLAIMER OF ALL WARRANTIES.
$Date: 2005-03-21 01:16:03 +1100 (Mon, 21 Mar 2005) $ PYTHON(1)
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