PYTHON(1) General Commands Manual 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 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
-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 inter‐
preter.
-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 exe‐
cuting 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
-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 warn‐
ings 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.
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 applica‐
tions.
ENVIRONMENT VARIABLES
PYTHONHOME
Change the location of the standard Python libraries. By default, the libraries are searched in ${pre‐
fix}/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 argu‐
ment 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 mod‐
ule documentation.
PYTHONOPTIMIZE
If this is set to a non-empty string it is equivalent to specifying the -O option. If set to an inte‐
ger, 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 inte‐
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 inte‐
ger, 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 sepa‐
rate 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: http://www.python.org/psf
INTERNET RESOURCES
Main website: http://www.python.org/
Documentation: http://docs.python.org/
Developer resources: http://docs.python.org/devguide/
Downloads: http://python.org/download/
Module repository: http://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)
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