PYTHON(1) User Commands PYTHON(1)

NAME

python - an interpreted, interactive, object-oriented programming
language

SYNOPSIS

python [ -B ] [ -d ] [ -E ] [ -h ] [ -i ] [ -m module-name ]
[ -O ] [ -OO ] [ -R ] [ -Q argument ] [ -s ] [ -S ] [ -t ] [
-u ]
[ -v ] [ -V ] [ -W argument ] [ -x ] [ -3 ] [ -? ]
[ -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, see 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

-B Don't write .py[co] files on import. See also
PYTHONDONTWRITEBYTECODE.

-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 , -? , --help
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.

-OO Discard docstrings in addition to the -O optimizations.

-R Turn on "hash randomization", so that the hash() values of
str, bytes and datetime objects are "salted" with an
unpredictable pseudo-random value. Although they remain
constant within an individual Python process, they are not
predictable between repeated invocations of Python.

This is intended to provide protection against a denial of
service caused by carefully-chosen inputs that exploit the
worst case performance of a dict construction, O(n^2)
complexity. See
http://www.ocert.org/advisories/ocert-2011-003.html for
details.

-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 Don't add user site directory to sys.path.

-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
xreadlines(), readlines() and file-object iterators ("for line
in sys.stdin") which is not influenced 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 , --version
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 warning 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 abbreviation): 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 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!

-3 Warn about Python 3.x incompatibilities that 2to3 cannot
trivially fix.

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 interpreter
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 exception). 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_prefix}. 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.

PYTHONDONTWRITEBYTECODE
If this is set to a non-empty string it is equivalent to
specifying the -B option (don't try to write .py[co] files).

PYTHONINSPECT
If this is set to a non-empty string it is equivalent to
specifying the -i option.

PYTHONIOENCODING
If this is set before running the interpreter, it overrides
the encoding used for stdin/stdout/stderr, in the syntax
encodingname:errorhandler The errorhandler part is optional
and has the same meaning as in str.encode. For stderr, the
errorhandler
part is ignored; the handler will always be
'backslashreplace'.

PYTHONNOUSERSITE
If this is set to a non-empty string it is equivalent to
specifying the -s option (Don't add the user site directory to
sys.path).

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.

PYTHONWARNINGS
If this is set to a comma-separated string it is equivalent to
specifying the -W option for each separate value.

PYTHONHASHSEED
If this variable is set to "random", the effect is the same as
specifying the -R option: a random value is used to seed the
hashes of str, bytes and datetime objects.

If PYTHONHASHSEED is set to an integer value, it is used as a
fixed seed for generating the hash() of the types covered by
the hash randomization. Its purpose is to allow repeatable
hashing, such as for selftests for the interpreter itself, or
to allow a cluster of python processes to share hash values.

The integer must be a decimal number in the range
[0,4294967295]. Specifying the value 0 will lead to the same
hash values as when hash randomization is disabled.

AUTHOR

The Python Software Foundation: https://www.python.org/psf/

INTERNET RESOURCES

Main website: https://www.python.org/
Documentation: https://docs.python.org/2/
Developer resources: https://docs.python.org/devguide/
Downloads: https://www.python.org/downloads/
Module repository: https://pypi.python.org/
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 distribution for information on terms
& conditions for accessing and otherwise using Python and for a
DISCLAIMER OF ALL WARRANTIES.

PYTHON(1)