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.
The simplest settings apply a particular action unconditionally to all warnings emitted by a process (even those that are otherwise ignored by default):
-Wdefault # Warn once per call location
-Werror # Convert to exceptions
-Walways # Warn every time
-Wmodule # Warn once per calling module
-Wonce # Warn once per Python process
-Wignore # Never warn
The action names can be abbreviated as desired and the interpreter will resolve them to the appropriate action name. For example, -Wi is the same as -Wignore .
The full form of argument is: action:message:category:module:lineno
Empty fields match all values; trailing empty fields may be omitted. For example -W ignore::DeprecationWarning ignores all DeprecationWarning warnings.
The action field is as explained above but only applies to warnings that match the remaining fields.
The message field must match the whole printed warning message; this match is case-insensitive.
The category field matches the warning category (ex: "DeprecationWarning"). 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 module field matches the (fully-qualified) module name; this match is case-sensitive.
The lineno field matches the line number, where zero matches all line numbers and is thus equivalent to an omitted line number.
Multiple -W options can be given; when a warning matches more than one option, the action for the last matching option is performed. Invalid -W options are ignored (though, a warning message is printed about invalid options when the first warning is issued).
Warnings can also be controlled using the PYTHONWARNINGS environment variable and from within a Python program using the warnings module. For example, the warnings.filterwarnings() function can be used to use a regular expression on the warning message.
-X faulthandler: enable faulthandler
-X showrefcount: output the total reference count and number of used
memory blocks when the program finishes or after each statement in the
interactive interpreter. This only works on debug builds
-X tracemalloc: start tracing Python memory allocations using the
tracemalloc module. By default, only the most recent frame is stored in a
traceback of a trace. Use -X tracemalloc=NFRAME to start tracing with a
traceback limit of NFRAME frames
-X importtime: show how long each import takes. It shows module name,
cumulative time (including nested imports) and self time (excluding
nested imports). Note that its output may be broken in multi-threaded
application. Typical usage is python3 -X importtime -c 'import asyncio'
-X dev: enable CPython's "development mode", introducing additional runtime
checks which are too expensive to be enabled by default. It will not be
more verbose than the default if the code is correct: new warnings are
only emitted when an issue is detected. Effect of the developer mode:
* Add default warning filter, as -W default
* Install debug hooks on memory allocators: see the PyMem_SetupDebugHooks() C function
* Enable the faulthandler module to dump the Python traceback on a crash
* Enable asyncio debug mode
* Set the dev_mode attribute of sys.flags to True
* io.IOBase destructor logs close() exceptions
-X utf8: enable UTF-8 mode for operating system interfaces, overriding the default
locale-aware mode. -X utf8=0 explicitly disables UTF-8 mode (even when it would
otherwise activate automatically). See PYTHONUTF8 for more details
-X pycache_prefix=PATH: enable writing .pyc files to a parallel tree rooted at the
given directory instead of to the code tree.
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.
${prefix}/lib/python<version>
${exec_prefix}/lib/python<version>
${prefix}/include/python<version>
${exec_prefix}/include/python<version>
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.