python3(1)
NAME
python - an interpreted, interactive, object-oriented programming language
SYNOPSIS
python [ -B ] [ -b ] [ -d ] [ -E ] [ -h ] [ -i ] [ -I ]
[ -m module-name ] [ -q ] [ -O ] [ -OO ] [ -s ] [ -S ] [ -u ]
[ -v ] [ -V ] [ -W argument ] [ -x ] [ [ -X option ] -? ]
[ -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 .pyc files on import. See also
PYTHONDONTWRITEBYTECODE.
-b Issue warnings about str(bytes_instance),
str(bytearray_instance) and comparing bytes/bytearray with str.
(-bb: issue errors)
-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.
-I Run Python in isolated mode. This also implies -E and -s. In
isolated mode sys.path contains neither the script's directory
nor the user's site-packages directory. All PYTHON* environment
variables are ignored, too. Further restrictions may be imposed
to prevent the user from injecting malicious code.
-m module-name
Searches sys.path for the named module and runs the
corresponding .py file as a script.
-O Turn on basic optimizations. Given twice, causes docstrings to
be discarded.
-OO Discard docstrings in addition to the -O optimizations.
-q Do not print the version and copyright messages. These messages
are also suppressed in non-interactive mode.
-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. Also disable these
manipulations if site is explicitly imported later.
-u Force the binary I/O layers of stdout and stderr to be
unbuffered. stdin is always buffered. The text I/O layer will
still be line-buffered.
-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 option
Set implementation specific option.
-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 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.
On Debian GNU/{Hurd,Linux} the default for both is /usr.
${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.
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.
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 .pyc 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", 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 disable hash
randomization.
AUTHOR
The Python Software Foundation: https://www.python.org/psf/
INTERNET RESOURCES
Main website: https://www.python.org/ Documentation: https://docs.python.org/ 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)
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