PYTHON(1) General Commands Manual PYTHON(1)
NAME
python - an interpreted, interactive, object-oriented programming lan-
guage
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 lan-
guage 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, con-
stants, 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 applica-
tions. 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 PYTHONDONTWRITE-
BYTECODE.
-c command
Specify the command to execute (see next section). This termi-
nates 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 correspond-
ing .py file as a script.
-O Turn on basic optimizations. This changes the filename exten-
sion 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 ser-
vice 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 xread-
lines(), 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 mod-
ule.
The simplest form of argument is one of the following action
strings (or a unique abbreviation): ignore to ignore all warn-
ings; default to explicitly request the default behavior (print-
ing each warning once per source line); all to print a warning
each time it occurs (this may generate many messages if a warn-
ing 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 excep-
tion instead of printing a warning message.
The full form of argument is action:message:category:mod-
ule: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 warn-
ing 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 num-
ber, 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 triv-
ially 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 multi-
ple statements separated by newlines. Leading whitespace is signifi-
cant 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 conven-
tions; ${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<ver-
sion> 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 ${pre-
fix}:${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 path-
names separated by colons. Non-existent directories are
silently ignored. The default search path is installation
dependent, but generally begins with ${prefix}/lib/python<ver-
sion> (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 speci-
fying 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 speci-
fying 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 speci-
fying 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 speci-
fying the -i option.
PYTHONIOENCODING
If this is set before running the interpreter, it overrides the
encoding used for stdin/stdout/stderr, in the syntax encoding-
name: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 speci-
fying 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 speci-
fying the -u option.
PYTHONVERBOSE
If this is set to a non-empty string it is equivalent to speci-
fying 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 DIS-
CLAIMER OF ALL WARRANTIES.
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