mirror of https://github.com/python/cpython
1219 lines
53 KiB
ReStructuredText
1219 lines
53 KiB
ReStructuredText
:mod:`sys` --- System-specific parameters and functions
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=======================================================
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.. module:: sys
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:synopsis: Access system-specific parameters and functions.
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This module provides access to some variables used or maintained by the
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interpreter and to functions that interact strongly with the interpreter. It is
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always available.
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.. data:: abiflags
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On POSIX systems where Python is build with the standard ``configure``
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script, this contains the ABI flags as specified by :pep:`3149`.
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.. versionadded:: 3.2
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.. data:: argv
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The list of command line arguments passed to a Python script. ``argv[0]`` is the
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script name (it is operating system dependent whether this is a full pathname or
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not). If the command was executed using the :option:`-c` command line option to
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the interpreter, ``argv[0]`` is set to the string ``'-c'``. If no script name
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was passed to the Python interpreter, ``argv[0]`` is the empty string.
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To loop over the standard input, or the list of files given on the
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command line, see the :mod:`fileinput` module.
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.. data:: base_exec_prefix
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Set during Python startup, before ``site.py`` is run, to the same value as
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:data:`exec_prefix`. If not running in a
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:ref:`virtual environment <venv-def>`, the values will stay the same; if
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``site.py`` finds that a virtual environment is in use, the values of
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:data:`prefix` and :data:`exec_prefix` will be changed to point to the
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virtual environment, whereas :data:`base_prefix` and
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:data:`base_exec_prefix` will remain pointing to the base Python
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installation (the one which the virtual environment was created from).
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.. versionadded:: 3.3
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.. data:: base_prefix
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Set during Python startup, before ``site.py`` is run, to the same value as
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:data:`prefix`. If not running in a :ref:`virtual environment <venv-def>`, the values
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will stay the same; if ``site.py`` finds that a virtual environment is in
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use, the values of :data:`prefix` and :data:`exec_prefix` will be changed to
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point to the virtual environment, whereas :data:`base_prefix` and
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:data:`base_exec_prefix` will remain pointing to the base Python
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installation (the one which the virtual environment was created from).
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.. versionadded:: 3.3
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.. data:: byteorder
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An indicator of the native byte order. This will have the value ``'big'`` on
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big-endian (most-significant byte first) platforms, and ``'little'`` on
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little-endian (least-significant byte first) platforms.
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.. data:: builtin_module_names
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A tuple of strings giving the names of all modules that are compiled into this
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Python interpreter. (This information is not available in any other way ---
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``modules.keys()`` only lists the imported modules.)
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.. function:: call_tracing(func, args)
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Call ``func(*args)``, while tracing is enabled. The tracing state is saved,
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and restored afterwards. This is intended to be called from a debugger from
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a checkpoint, to recursively debug some other code.
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.. data:: copyright
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A string containing the copyright pertaining to the Python interpreter.
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.. function:: _clear_type_cache()
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Clear the internal type cache. The type cache is used to speed up attribute
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and method lookups. Use the function *only* to drop unnecessary references
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during reference leak debugging.
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This function should be used for internal and specialized purposes only.
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.. function:: _current_frames()
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Return a dictionary mapping each thread's identifier to the topmost stack frame
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currently active in that thread at the time the function is called. Note that
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functions in the :mod:`traceback` module can build the call stack given such a
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frame.
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This is most useful for debugging deadlock: this function does not require the
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deadlocked threads' cooperation, and such threads' call stacks are frozen for as
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long as they remain deadlocked. The frame returned for a non-deadlocked thread
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may bear no relationship to that thread's current activity by the time calling
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code examines the frame.
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This function should be used for internal and specialized purposes only.
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.. function:: _debugmallocstats()
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Print low-level information to stderr about the state of CPython's memory
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allocator.
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If Python is configured --with-pydebug, it also performs some expensive
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internal consistency checks.
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.. versionadded:: 3.3
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.. impl-detail::
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This function is specific to CPython. The exact output format is not
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defined here, and may change.
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.. data:: dllhandle
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Integer specifying the handle of the Python DLL. Availability: Windows.
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.. function:: displayhook(value)
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If *value* is not ``None``, this function prints ``repr(value)`` to
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``sys.stdout``, and saves *value* in ``builtins._``. If ``repr(value)`` is
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not encodable to ``sys.stdout.encoding`` with ``sys.stdout.errors`` error
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handler (which is probably ``'strict'``), encode it to
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``sys.stdout.encoding`` with ``'backslashreplace'`` error handler.
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``sys.displayhook`` is called on the result of evaluating an :term:`expression`
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entered in an interactive Python session. The display of these values can be
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customized by assigning another one-argument function to ``sys.displayhook``.
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Pseudo-code::
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def displayhook(value):
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if value is None:
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return
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# Set '_' to None to avoid recursion
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builtins._ = None
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text = repr(value)
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try:
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sys.stdout.write(text)
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except UnicodeEncodeError:
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bytes = text.encode(sys.stdout.encoding, 'backslashreplace')
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if hasattr(sys.stdout, 'buffer'):
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sys.stdout.buffer.write(bytes)
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else:
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text = bytes.decode(sys.stdout.encoding, 'strict')
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sys.stdout.write(text)
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sys.stdout.write("\n")
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builtins._ = value
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.. versionchanged:: 3.2
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Use ``'backslashreplace'`` error handler on :exc:`UnicodeEncodeError`.
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.. data:: dont_write_bytecode
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If this is true, Python won't try to write ``.pyc`` or ``.pyo`` files on the
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import of source modules. This value is initially set to ``True`` or
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``False`` depending on the :option:`-B` command line option and the
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:envvar:`PYTHONDONTWRITEBYTECODE` environment variable, but you can set it
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yourself to control bytecode file generation.
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.. function:: excepthook(type, value, traceback)
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This function prints out a given traceback and exception to ``sys.stderr``.
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When an exception is raised and uncaught, the interpreter calls
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``sys.excepthook`` with three arguments, the exception class, exception
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instance, and a traceback object. In an interactive session this happens just
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before control is returned to the prompt; in a Python program this happens just
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before the program exits. The handling of such top-level exceptions can be
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customized by assigning another three-argument function to ``sys.excepthook``.
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.. data:: __displayhook__
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__excepthook__
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These objects contain the original values of ``displayhook`` and ``excepthook``
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at the start of the program. They are saved so that ``displayhook`` and
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``excepthook`` can be restored in case they happen to get replaced with broken
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objects.
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.. function:: exc_info()
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This function returns a tuple of three values that give information about the
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exception that is currently being handled. The information returned is specific
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both to the current thread and to the current stack frame. If the current stack
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frame is not handling an exception, the information is taken from the calling
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stack frame, or its caller, and so on until a stack frame is found that is
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handling an exception. Here, "handling an exception" is defined as "executing
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an except clause." For any stack frame, only information about the exception
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being currently handled is accessible.
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.. index:: object: traceback
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If no exception is being handled anywhere on the stack, a tuple containing
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three ``None`` values is returned. Otherwise, the values returned are
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``(type, value, traceback)``. Their meaning is: *type* gets the type of the
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exception being handled (a subclass of :exc:`BaseException`); *value* gets
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the exception instance (an instance of the exception type); *traceback* gets
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a traceback object (see the Reference Manual) which encapsulates the call
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stack at the point where the exception originally occurred.
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.. warning::
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Assigning the *traceback* return value to a local variable in a function
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that is handling an exception will cause a circular reference. Since most
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functions don't need access to the traceback, the best solution is to use
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something like ``exctype, value = sys.exc_info()[:2]`` to extract only the
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exception type and value. If you do need the traceback, make sure to
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delete it after use (best done with a :keyword:`try`
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... :keyword:`finally` statement) or to call :func:`exc_info` in a
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function that does not itself handle an exception.
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Such cycles are normally automatically reclaimed when garbage collection
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is enabled and they become unreachable, but it remains more efficient to
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avoid creating cycles.
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.. data:: exec_prefix
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A string giving the site-specific directory prefix where the platform-dependent
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Python files are installed; by default, this is also ``'/usr/local'``. This can
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be set at build time with the ``--exec-prefix`` argument to the
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:program:`configure` script. Specifically, all configuration files (e.g. the
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:file:`pyconfig.h` header file) are installed in the directory
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:file:`{exec_prefix}/lib/python{X.Y}/config`, and shared library modules are
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installed in :file:`{exec_prefix}/lib/python{X.Y}/lib-dynload`, where *X.Y*
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is the version number of Python, for example ``3.2``.
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.. note:: If a :ref:`virtual environment <venv-def>` is in effect, this
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value will be changed in ``site.py`` to point to the virtual environment.
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The value for the Python installation will still be available, via
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:data:`base_exec_prefix`.
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.. data:: executable
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A string giving the absolute path of the executable binary for the Python
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interpreter, on systems where this makes sense. If Python is unable to retrieve
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the real path to its executable, :data:`sys.executable` will be an empty string
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or ``None``.
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.. function:: exit([arg])
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Exit from Python. This is implemented by raising the :exc:`SystemExit`
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exception, so cleanup actions specified by finally clauses of :keyword:`try`
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statements are honored, and it is possible to intercept the exit attempt at
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an outer level.
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The optional argument *arg* can be an integer giving the exit status
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(defaulting to zero), or another type of object. If it is an integer, zero
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is considered "successful termination" and any nonzero value is considered
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"abnormal termination" by shells and the like. Most systems require it to be
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in the range 0-127, and produce undefined results otherwise. Some systems
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have a convention for assigning specific meanings to specific exit codes, but
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these are generally underdeveloped; Unix programs generally use 2 for command
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line syntax errors and 1 for all other kind of errors. If another type of
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object is passed, ``None`` is equivalent to passing zero, and any other
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object is printed to :data:`stderr` and results in an exit code of 1. In
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particular, ``sys.exit("some error message")`` is a quick way to exit a
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program when an error occurs.
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Since :func:`exit` ultimately "only" raises an exception, it will only exit
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the process when called from the main thread, and the exception is not
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intercepted.
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.. data:: flags
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The :term:`struct sequence` *flags* exposes the status of command line
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flags. The attributes are read only.
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============================= =============================
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attribute flag
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============================= =============================
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:const:`debug` :option:`-d`
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:const:`inspect` :option:`-i`
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:const:`interactive` :option:`-i`
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:const:`optimize` :option:`-O` or :option:`-OO`
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:const:`dont_write_bytecode` :option:`-B`
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:const:`no_user_site` :option:`-s`
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:const:`no_site` :option:`-S`
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:const:`ignore_environment` :option:`-E`
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:const:`verbose` :option:`-v`
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:const:`bytes_warning` :option:`-b`
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:const:`quiet` :option:`-q`
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:const:`hash_randomization` :option:`-R`
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============================= =============================
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.. versionchanged:: 3.2
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Added ``quiet`` attribute for the new :option:`-q` flag.
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.. versionadded:: 3.2.3
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The ``hash_randomization`` attribute.
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.. versionchanged:: 3.3
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Removed obsolete ``division_warning`` attribute.
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.. data:: float_info
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A :term:`struct sequence` holding information about the float type. It
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contains low level information about the precision and internal
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representation. The values correspond to the various floating-point
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constants defined in the standard header file :file:`float.h` for the 'C'
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programming language; see section 5.2.4.2.2 of the 1999 ISO/IEC C standard
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[C99]_, 'Characteristics of floating types', for details.
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+---------------------+----------------+--------------------------------------------------+
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| attribute | float.h macro | explanation |
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+=====================+================+==================================================+
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| :const:`epsilon` | DBL_EPSILON | difference between 1 and the least value greater |
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| | | than 1 that is representable as a float |
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+---------------------+----------------+--------------------------------------------------+
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| :const:`dig` | DBL_DIG | maximum number of decimal digits that can be |
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| | | faithfully represented in a float; see below |
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+---------------------+----------------+--------------------------------------------------+
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| :const:`mant_dig` | DBL_MANT_DIG | float precision: the number of base-``radix`` |
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| | | digits in the significand of a float |
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+---------------------+----------------+--------------------------------------------------+
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| :const:`max` | DBL_MAX | maximum representable finite float |
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+---------------------+----------------+--------------------------------------------------+
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| :const:`max_exp` | DBL_MAX_EXP | maximum integer e such that ``radix**(e-1)`` is |
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| | | a representable finite float |
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+---------------------+----------------+--------------------------------------------------+
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| :const:`max_10_exp` | DBL_MAX_10_EXP | maximum integer e such that ``10**e`` is in the |
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| | | range of representable finite floats |
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+---------------------+----------------+--------------------------------------------------+
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| :const:`min` | DBL_MIN | minimum positive normalized float |
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+---------------------+----------------+--------------------------------------------------+
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| :const:`min_exp` | DBL_MIN_EXP | minimum integer e such that ``radix**(e-1)`` is |
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| | | a normalized float |
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+---------------------+----------------+--------------------------------------------------+
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| :const:`min_10_exp` | DBL_MIN_10_EXP | minimum integer e such that ``10**e`` is a |
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| | | normalized float |
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+---------------------+----------------+--------------------------------------------------+
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| :const:`radix` | FLT_RADIX | radix of exponent representation |
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+---------------------+----------------+--------------------------------------------------+
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| :const:`rounds` | FLT_ROUNDS | integer constant representing the rounding mode |
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| | | used for arithmetic operations. This reflects |
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| | | the value of the system FLT_ROUNDS macro at |
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| | | interpreter startup time. See section 5.2.4.2.2 |
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| | | of the C99 standard for an explanation of the |
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| | | possible values and their meanings. |
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+---------------------+----------------+--------------------------------------------------+
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The attribute :attr:`sys.float_info.dig` needs further explanation. If
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``s`` is any string representing a decimal number with at most
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:attr:`sys.float_info.dig` significant digits, then converting ``s`` to a
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float and back again will recover a string representing the same decimal
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value::
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>>> import sys
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>>> sys.float_info.dig
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15
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>>> s = '3.14159265358979' # decimal string with 15 significant digits
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>>> format(float(s), '.15g') # convert to float and back -> same value
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'3.14159265358979'
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But for strings with more than :attr:`sys.float_info.dig` significant digits,
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this isn't always true::
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>>> s = '9876543211234567' # 16 significant digits is too many!
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>>> format(float(s), '.16g') # conversion changes value
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'9876543211234568'
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.. data:: float_repr_style
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A string indicating how the :func:`repr` function behaves for
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floats. If the string has value ``'short'`` then for a finite
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float ``x``, ``repr(x)`` aims to produce a short string with the
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property that ``float(repr(x)) == x``. This is the usual behaviour
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in Python 3.1 and later. Otherwise, ``float_repr_style`` has value
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``'legacy'`` and ``repr(x)`` behaves in the same way as it did in
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versions of Python prior to 3.1.
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.. versionadded:: 3.1
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.. function:: getcheckinterval()
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Return the interpreter's "check interval"; see :func:`setcheckinterval`.
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.. deprecated:: 3.2
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Use :func:`getswitchinterval` instead.
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.. function:: getdefaultencoding()
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Return the name of the current default string encoding used by the Unicode
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implementation.
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.. function:: getdlopenflags()
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Return the current value of the flags that are used for :c:func:`dlopen` calls.
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The flag constants are defined in the :mod:`ctypes` and :mod:`DLFCN` modules.
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Availability: Unix.
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.. function:: getfilesystemencoding()
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Return the name of the encoding used to convert Unicode filenames into
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system file names. The result value depends on the operating system:
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* On Mac OS X, the encoding is ``'utf-8'``.
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* On Unix, the encoding is the user's preference according to the result of
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nl_langinfo(CODESET), or ``'utf-8'`` if ``nl_langinfo(CODESET)`` failed.
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* On Windows NT+, file names are Unicode natively, so no conversion is
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performed. :func:`getfilesystemencoding` still returns ``'mbcs'``, as
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this is the encoding that applications should use when they explicitly
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want to convert Unicode strings to byte strings that are equivalent when
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used as file names.
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* On Windows 9x, the encoding is ``'mbcs'``.
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.. versionchanged:: 3.2
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On Unix, use ``'utf-8'`` instead of ``None`` if ``nl_langinfo(CODESET)``
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failed. :func:`getfilesystemencoding` result cannot be ``None``.
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.. function:: getrefcount(object)
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Return the reference count of the *object*. The count returned is generally one
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higher than you might expect, because it includes the (temporary) reference as
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an argument to :func:`getrefcount`.
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.. function:: getrecursionlimit()
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Return the current value of the recursion limit, the maximum depth of the Python
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interpreter stack. This limit prevents infinite recursion from causing an
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overflow of the C stack and crashing Python. It can be set by
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:func:`setrecursionlimit`.
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.. function:: getsizeof(object[, default])
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Return the size of an object in bytes. The object can be any type of
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object. All built-in objects will return correct results, but this
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does not have to hold true for third-party extensions as it is implementation
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specific.
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Only the memory consumption directly attributed to the object is
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accounted for, not the memory consumption of objects it refers to.
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If given, *default* will be returned if the object does not provide means to
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retrieve the size. Otherwise a :exc:`TypeError` will be raised.
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:func:`getsizeof` calls the object's ``__sizeof__`` method and adds an
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additional garbage collector overhead if the object is managed by the garbage
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collector.
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See `recursive sizeof recipe <http://code.activestate.com/recipes/577504>`_
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for an example of using :func:`getsizeof` recursively to find the size of
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containers and all their contents.
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.. function:: getswitchinterval()
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Return the interpreter's "thread switch interval"; see
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:func:`setswitchinterval`.
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.. versionadded:: 3.2
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.. function:: _getframe([depth])
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Return a frame object from the call stack. If optional integer *depth* is
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given, return the frame object that many calls below the top of the stack. If
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that is deeper than the call stack, :exc:`ValueError` is raised. The default
|
|
for *depth* is zero, returning the frame at the top of the call stack.
|
|
|
|
.. impl-detail::
|
|
|
|
This function should be used for internal and specialized purposes only.
|
|
It is not guaranteed to exist in all implementations of Python.
|
|
|
|
|
|
.. function:: getprofile()
|
|
|
|
.. index::
|
|
single: profile function
|
|
single: profiler
|
|
|
|
Get the profiler function as set by :func:`setprofile`.
|
|
|
|
|
|
.. function:: gettrace()
|
|
|
|
.. index::
|
|
single: trace function
|
|
single: debugger
|
|
|
|
Get the trace function as set by :func:`settrace`.
|
|
|
|
.. impl-detail::
|
|
|
|
The :func:`gettrace` function is intended only for implementing debuggers,
|
|
profilers, coverage tools and the like. Its behavior is part of the
|
|
implementation platform, rather than part of the language definition, and
|
|
thus may not be available in all Python implementations.
|
|
|
|
|
|
.. function:: getwindowsversion()
|
|
|
|
Return a named tuple describing the Windows version
|
|
currently running. The named elements are *major*, *minor*,
|
|
*build*, *platform*, *service_pack*, *service_pack_minor*,
|
|
*service_pack_major*, *suite_mask*, and *product_type*.
|
|
*service_pack* contains a string while all other values are
|
|
integers. The components can also be accessed by name, so
|
|
``sys.getwindowsversion()[0]`` is equivalent to
|
|
``sys.getwindowsversion().major``. For compatibility with prior
|
|
versions, only the first 5 elements are retrievable by indexing.
|
|
|
|
*platform* may be one of the following values:
|
|
|
|
+-----------------------------------------+-------------------------+
|
|
| Constant | Platform |
|
|
+=========================================+=========================+
|
|
| :const:`0 (VER_PLATFORM_WIN32s)` | Win32s on Windows 3.1 |
|
|
+-----------------------------------------+-------------------------+
|
|
| :const:`1 (VER_PLATFORM_WIN32_WINDOWS)` | Windows 95/98/ME |
|
|
+-----------------------------------------+-------------------------+
|
|
| :const:`2 (VER_PLATFORM_WIN32_NT)` | Windows NT/2000/XP/x64 |
|
|
+-----------------------------------------+-------------------------+
|
|
| :const:`3 (VER_PLATFORM_WIN32_CE)` | Windows CE |
|
|
+-----------------------------------------+-------------------------+
|
|
|
|
*product_type* may be one of the following values:
|
|
|
|
+---------------------------------------+---------------------------------+
|
|
| Constant | Meaning |
|
|
+=======================================+=================================+
|
|
| :const:`1 (VER_NT_WORKSTATION)` | The system is a workstation. |
|
|
+---------------------------------------+---------------------------------+
|
|
| :const:`2 (VER_NT_DOMAIN_CONTROLLER)` | The system is a domain |
|
|
| | controller. |
|
|
+---------------------------------------+---------------------------------+
|
|
| :const:`3 (VER_NT_SERVER)` | The system is a server, but not |
|
|
| | a domain controller. |
|
|
+---------------------------------------+---------------------------------+
|
|
|
|
|
|
This function wraps the Win32 :c:func:`GetVersionEx` function; see the
|
|
Microsoft documentation on :c:func:`OSVERSIONINFOEX` for more information
|
|
about these fields.
|
|
|
|
Availability: Windows.
|
|
|
|
.. versionchanged:: 3.2
|
|
Changed to a named tuple and added *service_pack_minor*,
|
|
*service_pack_major*, *suite_mask*, and *product_type*.
|
|
|
|
|
|
.. data:: hash_info
|
|
|
|
A :term:`struct sequence` giving parameters of the numeric hash
|
|
implementation. For more details about hashing of numeric types, see
|
|
:ref:`numeric-hash`.
|
|
|
|
+---------------------+--------------------------------------------------+
|
|
| attribute | explanation |
|
|
+=====================+==================================================+
|
|
| :const:`width` | width in bits used for hash values |
|
|
+---------------------+--------------------------------------------------+
|
|
| :const:`modulus` | prime modulus P used for numeric hash scheme |
|
|
+---------------------+--------------------------------------------------+
|
|
| :const:`inf` | hash value returned for a positive infinity |
|
|
+---------------------+--------------------------------------------------+
|
|
| :const:`nan` | hash value returned for a nan |
|
|
+---------------------+--------------------------------------------------+
|
|
| :const:`imag` | multiplier used for the imaginary part of a |
|
|
| | complex number |
|
|
+---------------------+--------------------------------------------------+
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
|
|
.. data:: hexversion
|
|
|
|
The version number encoded as a single integer. This is guaranteed to increase
|
|
with each version, including proper support for non-production releases. For
|
|
example, to test that the Python interpreter is at least version 1.5.2, use::
|
|
|
|
if sys.hexversion >= 0x010502F0:
|
|
# use some advanced feature
|
|
...
|
|
else:
|
|
# use an alternative implementation or warn the user
|
|
...
|
|
|
|
This is called ``hexversion`` since it only really looks meaningful when viewed
|
|
as the result of passing it to the built-in :func:`hex` function. The
|
|
:term:`struct sequence` :data:`sys.version_info` may be used for a more
|
|
human-friendly encoding of the same information.
|
|
|
|
The ``hexversion`` is a 32-bit number with the following layout:
|
|
|
|
+-------------------------+------------------------------------------------+
|
|
| Bits (big endian order) | Meaning |
|
|
+=========================+================================================+
|
|
| :const:`1-8` | ``PY_MAJOR_VERSION`` (the ``2`` in |
|
|
| | ``2.1.0a3``) |
|
|
+-------------------------+------------------------------------------------+
|
|
| :const:`9-16` | ``PY_MINOR_VERSION`` (the ``1`` in |
|
|
| | ``2.1.0a3``) |
|
|
+-------------------------+------------------------------------------------+
|
|
| :const:`17-24` | ``PY_MICRO_VERSION`` (the ``0`` in |
|
|
| | ``2.1.0a3``) |
|
|
+-------------------------+------------------------------------------------+
|
|
| :const:`25-28` | ``PY_RELEASE_LEVEL`` (``0xA`` for alpha, |
|
|
| | ``0xB`` for beta, ``0xC`` for release |
|
|
| | candidate and ``0xF`` for final) |
|
|
+-------------------------+------------------------------------------------+
|
|
| :const:`29-32` | ``PY_RELEASE_SERIAL`` (the ``3`` in |
|
|
| | ``2.1.0a3``, zero for final releases) |
|
|
+-------------------------+------------------------------------------------+
|
|
|
|
Thus ``2.1.0a3`` is hexversion ``0x020100a3``.
|
|
|
|
|
|
.. data:: implementation
|
|
|
|
An object containing information about the implementation of the
|
|
currently running Python interpreter. The following attributes are
|
|
required to exist in all Python implementations.
|
|
|
|
*name* is the implementation's identifier, e.g. ``'cpython'``. The actual
|
|
string is defined by the Python implementation, but it is guaranteed to be
|
|
lower case.
|
|
|
|
*version* is a named tuple, in the same format as
|
|
:data:`sys.version_info`. It represents the version of the Python
|
|
*implementation*. This has a distinct meaning from the specific
|
|
version of the Python *language* to which the currently running
|
|
interpreter conforms, which ``sys.version_info`` represents. For
|
|
example, for PyPy 1.8 ``sys.implementation.version`` might be
|
|
``sys.version_info(1, 8, 0, 'final', 0)``, whereas ``sys.version_info``
|
|
would be ``sys.version_info(2, 7, 2, 'final', 0)``. For CPython they
|
|
are the same value, since it is the reference implementation.
|
|
|
|
*hexversion* is the implementation version in hexadecimal format, like
|
|
:data:`sys.hexversion`.
|
|
|
|
*cache_tag* is the tag used by the import machinery in the filenames of
|
|
cached modules. By convention, it would be a composite of the
|
|
implementation's name and version, like ``'cpython-33'``. However, a
|
|
Python implementation may use some other value if appropriate. If
|
|
``cache_tag`` is set to ``None``, it indicates that module caching should
|
|
be disabled.
|
|
|
|
:data:`sys.implementation` may contain additional attributes specific to
|
|
the Python implementation. These non-standard attributes must start with
|
|
an underscore, and are not described here. Regardless of its contents,
|
|
:data:`sys.implementation` will not change during a run of the interpreter,
|
|
nor between implementation versions. (It may change between Python
|
|
language versions, however.) See `PEP 421` for more information.
|
|
|
|
.. versionadded:: 3.3
|
|
|
|
|
|
.. data:: int_info
|
|
|
|
A :term:`struct sequence` that holds information about Python's internal
|
|
representation of integers. The attributes are read only.
|
|
|
|
+-------------------------+----------------------------------------------+
|
|
| Attribute | Explanation |
|
|
+=========================+==============================================+
|
|
| :const:`bits_per_digit` | number of bits held in each digit. Python |
|
|
| | integers are stored internally in base |
|
|
| | ``2**int_info.bits_per_digit`` |
|
|
+-------------------------+----------------------------------------------+
|
|
| :const:`sizeof_digit` | size in bytes of the C type used to |
|
|
| | represent a digit |
|
|
+-------------------------+----------------------------------------------+
|
|
|
|
.. versionadded:: 3.1
|
|
|
|
|
|
.. function:: intern(string)
|
|
|
|
Enter *string* in the table of "interned" strings and return the interned string
|
|
-- which is *string* itself or a copy. Interning strings is useful to gain a
|
|
little performance on dictionary lookup -- if the keys in a dictionary are
|
|
interned, and the lookup key is interned, the key comparisons (after hashing)
|
|
can be done by a pointer compare instead of a string compare. Normally, the
|
|
names used in Python programs are automatically interned, and the dictionaries
|
|
used to hold module, class or instance attributes have interned keys.
|
|
|
|
Interned strings are not immortal; you must keep a reference to the return
|
|
value of :func:`intern` around to benefit from it.
|
|
|
|
|
|
.. data:: last_type
|
|
last_value
|
|
last_traceback
|
|
|
|
These three variables are not always defined; they are set when an exception is
|
|
not handled and the interpreter prints an error message and a stack traceback.
|
|
Their intended use is to allow an interactive user to import a debugger module
|
|
and engage in post-mortem debugging without having to re-execute the command
|
|
that caused the error. (Typical use is ``import pdb; pdb.pm()`` to enter the
|
|
post-mortem debugger; see :mod:`pdb` module for
|
|
more information.)
|
|
|
|
The meaning of the variables is the same as that of the return values from
|
|
:func:`exc_info` above.
|
|
|
|
|
|
.. data:: maxsize
|
|
|
|
An integer giving the maximum value a variable of type :c:type:`Py_ssize_t` can
|
|
take. It's usually ``2**31 - 1`` on a 32-bit platform and ``2**63 - 1`` on a
|
|
64-bit platform.
|
|
|
|
|
|
.. data:: maxunicode
|
|
|
|
An integer giving the value of the largest Unicode code point,
|
|
i.e. ``1114111`` (``0x10FFFF`` in hexadecimal).
|
|
|
|
.. versionchanged:: 3.3
|
|
Before :pep:`393`, ``sys.maxunicode`` used to be either ``0xFFFF``
|
|
or ``0x10FFFF``, depending on the configuration option that specified
|
|
whether Unicode characters were stored as UCS-2 or UCS-4.
|
|
|
|
|
|
.. data:: meta_path
|
|
|
|
A list of :term:`finder` objects that have their :meth:`find_module`
|
|
methods called to see if one of the objects can find the module to be
|
|
imported. The :meth:`find_module` method is called at least with the
|
|
absolute name of the module being imported. If the module to be imported is
|
|
contained in package then the parent package's :attr:`__path__` attribute
|
|
is passed in as a second argument. The method returns ``None`` if
|
|
the module cannot be found, else returns a :term:`loader`.
|
|
|
|
:data:`sys.meta_path` is searched before any implicit default finders or
|
|
:data:`sys.path`.
|
|
|
|
See :pep:`302` for the original specification.
|
|
|
|
|
|
.. data:: modules
|
|
|
|
This is a dictionary that maps module names to modules which have already been
|
|
loaded. This can be manipulated to force reloading of modules and other tricks.
|
|
|
|
|
|
.. data:: path
|
|
|
|
.. index:: triple: module; search; path
|
|
|
|
A list of strings that specifies the search path for modules. Initialized from
|
|
the environment variable :envvar:`PYTHONPATH`, plus an installation-dependent
|
|
default.
|
|
|
|
As initialized upon program startup, the first item of this list, ``path[0]``,
|
|
is the directory containing the script that was used to invoke the Python
|
|
interpreter. If the script directory is not available (e.g. if the interpreter
|
|
is invoked interactively or if the script is read from standard input),
|
|
``path[0]`` is the empty string, which directs Python to search modules in the
|
|
current directory first. Notice that the script directory is inserted *before*
|
|
the entries inserted as a result of :envvar:`PYTHONPATH`.
|
|
|
|
A program is free to modify this list for its own purposes. Only strings
|
|
and bytes should be added to :data:`sys.path`; all other data types are
|
|
ignored during import.
|
|
|
|
|
|
.. seealso::
|
|
Module :mod:`site` This describes how to use .pth files to extend
|
|
:data:`sys.path`.
|
|
|
|
|
|
.. data:: path_hooks
|
|
|
|
A list of callables that take a path argument to try to create a
|
|
:term:`finder` for the path. If a finder can be created, it is to be
|
|
returned by the callable, else raise :exc:`ImportError`.
|
|
|
|
Originally specified in :pep:`302`.
|
|
|
|
|
|
.. data:: path_importer_cache
|
|
|
|
A dictionary acting as a cache for :term:`finder` objects. The keys are
|
|
paths that have been passed to :data:`sys.path_hooks` and the values are
|
|
the finders that are found. If a path is a valid file system path but no
|
|
explicit finder is found on :data:`sys.path_hooks` then ``None`` is
|
|
stored to represent the implicit default finder should be used. If the path
|
|
is not an existing path then :class:`imp.NullImporter` is set.
|
|
|
|
Originally specified in :pep:`302`.
|
|
|
|
|
|
.. data:: platform
|
|
|
|
This string contains a platform identifier that can be used to append
|
|
platform-specific components to :data:`sys.path`, for instance.
|
|
|
|
For Unix systems, except on Linux, this is the lowercased OS name as
|
|
returned by ``uname -s`` with the first part of the version as returned by
|
|
``uname -r`` appended, e.g. ``'sunos5'`` or ``'freebsd8'``, *at the time
|
|
when Python was built*. Unless you want to test for a specific system
|
|
version, it is therefore recommended to use the following idiom::
|
|
|
|
if sys.platform.startswith('freebsd'):
|
|
# FreeBSD-specific code here...
|
|
elif sys.platform.startswith('linux'):
|
|
# Linux-specific code here...
|
|
|
|
For other systems, the values are:
|
|
|
|
================ ===========================
|
|
System ``platform`` value
|
|
================ ===========================
|
|
Linux ``'linux'``
|
|
Windows ``'win32'``
|
|
Windows/Cygwin ``'cygwin'``
|
|
Mac OS X ``'darwin'``
|
|
OS/2 ``'os2'``
|
|
OS/2 EMX ``'os2emx'``
|
|
================ ===========================
|
|
|
|
.. versionchanged:: 3.3
|
|
On Linux, :attr:`sys.platform` doesn't contain the major version anymore.
|
|
It is always ``'linux'``, instead of ``'linux2'`` or ``'linux3'``. Since
|
|
older Python versions include the version number, it is recommended to
|
|
always use the ``startswith`` idiom presented above.
|
|
|
|
.. seealso::
|
|
|
|
:attr:`os.name` has a coarser granularity. :func:`os.uname` gives
|
|
system-dependent version information.
|
|
|
|
The :mod:`platform` module provides detailed checks for the
|
|
system's identity.
|
|
|
|
|
|
.. data:: prefix
|
|
|
|
A string giving the site-specific directory prefix where the platform
|
|
independent Python files are installed; by default, this is the string
|
|
``'/usr/local'``. This can be set at build time with the ``--prefix``
|
|
argument to the :program:`configure` script. The main collection of Python
|
|
library modules is installed in the directory :file:`{prefix}/lib/python{X.Y}`
|
|
while the platform independent header files (all except :file:`pyconfig.h`) are
|
|
stored in :file:`{prefix}/include/python{X.Y}`, where *X.Y* is the version
|
|
number of Python, for example ``3.2``.
|
|
|
|
.. note:: If a :ref:`virtual environment <venv-def>` is in effect, this
|
|
value will be changed in ``site.py`` to point to the virtual
|
|
environment. The value for the Python installation will still be
|
|
available, via :data:`base_prefix`.
|
|
|
|
|
|
.. data:: ps1
|
|
ps2
|
|
|
|
.. index::
|
|
single: interpreter prompts
|
|
single: prompts, interpreter
|
|
|
|
Strings specifying the primary and secondary prompt of the interpreter. These
|
|
are only defined if the interpreter is in interactive mode. Their initial
|
|
values in this case are ``'>>> '`` and ``'... '``. If a non-string object is
|
|
assigned to either variable, its :func:`str` is re-evaluated each time the
|
|
interpreter prepares to read a new interactive command; this can be used to
|
|
implement a dynamic prompt.
|
|
|
|
|
|
.. function:: setcheckinterval(interval)
|
|
|
|
Set the interpreter's "check interval". This integer value determines how often
|
|
the interpreter checks for periodic things such as thread switches and signal
|
|
handlers. The default is ``100``, meaning the check is performed every 100
|
|
Python virtual instructions. Setting it to a larger value may increase
|
|
performance for programs using threads. Setting it to a value ``<=`` 0 checks
|
|
every virtual instruction, maximizing responsiveness as well as overhead.
|
|
|
|
.. deprecated:: 3.2
|
|
This function doesn't have an effect anymore, as the internal logic for
|
|
thread switching and asynchronous tasks has been rewritten. Use
|
|
:func:`setswitchinterval` instead.
|
|
|
|
|
|
.. function:: setdlopenflags(n)
|
|
|
|
Set the flags used by the interpreter for :c:func:`dlopen` calls, such as when
|
|
the interpreter loads extension modules. Among other things, this will enable a
|
|
lazy resolving of symbols when importing a module, if called as
|
|
``sys.setdlopenflags(0)``. To share symbols across extension modules, call as
|
|
``sys.setdlopenflags(os.RTLD_GLOBAL)``. Symbolic names for the flag modules
|
|
can be found in the :mod:`os` module (``RTLD_xxx`` constants, e.g.
|
|
:data:`os.RTLD_LAZY`).
|
|
|
|
Availability: Unix.
|
|
|
|
.. function:: setprofile(profilefunc)
|
|
|
|
.. index::
|
|
single: profile function
|
|
single: profiler
|
|
|
|
Set the system's profile function, which allows you to implement a Python source
|
|
code profiler in Python. See chapter :ref:`profile` for more information on the
|
|
Python profiler. The system's profile function is called similarly to the
|
|
system's trace function (see :func:`settrace`), but it isn't called for each
|
|
executed line of code (only on call and return, but the return event is reported
|
|
even when an exception has been set). The function is thread-specific, but
|
|
there is no way for the profiler to know about context switches between threads,
|
|
so it does not make sense to use this in the presence of multiple threads. Also,
|
|
its return value is not used, so it can simply return ``None``.
|
|
|
|
|
|
.. function:: setrecursionlimit(limit)
|
|
|
|
Set the maximum depth of the Python interpreter stack to *limit*. This limit
|
|
prevents infinite recursion from causing an overflow of the C stack and crashing
|
|
Python.
|
|
|
|
The highest possible limit is platform-dependent. A user may need to set the
|
|
limit higher when they have a program that requires deep recursion and a platform
|
|
that supports a higher limit. This should be done with care, because a too-high
|
|
limit can lead to a crash.
|
|
|
|
|
|
.. function:: setswitchinterval(interval)
|
|
|
|
Set the interpreter's thread switch interval (in seconds). This floating-point
|
|
value determines the ideal duration of the "timeslices" allocated to
|
|
concurrently running Python threads. Please note that the actual value
|
|
can be higher, especially if long-running internal functions or methods
|
|
are used. Also, which thread becomes scheduled at the end of the interval
|
|
is the operating system's decision. The interpreter doesn't have its
|
|
own scheduler.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
|
|
.. function:: settrace(tracefunc)
|
|
|
|
.. index::
|
|
single: trace function
|
|
single: debugger
|
|
|
|
Set the system's trace function, which allows you to implement a Python
|
|
source code debugger in Python. The function is thread-specific; for a
|
|
debugger to support multiple threads, it must be registered using
|
|
:func:`settrace` for each thread being debugged.
|
|
|
|
Trace functions should have three arguments: *frame*, *event*, and
|
|
*arg*. *frame* is the current stack frame. *event* is a string: ``'call'``,
|
|
``'line'``, ``'return'``, ``'exception'``, ``'c_call'``, ``'c_return'``, or
|
|
``'c_exception'``. *arg* depends on the event type.
|
|
|
|
The trace function is invoked (with *event* set to ``'call'``) whenever a new
|
|
local scope is entered; it should return a reference to a local trace
|
|
function to be used that scope, or ``None`` if the scope shouldn't be traced.
|
|
|
|
The local trace function should return a reference to itself (or to another
|
|
function for further tracing in that scope), or ``None`` to turn off tracing
|
|
in that scope.
|
|
|
|
The events have the following meaning:
|
|
|
|
``'call'``
|
|
A function is called (or some other code block entered). The
|
|
global trace function is called; *arg* is ``None``; the return value
|
|
specifies the local trace function.
|
|
|
|
``'line'``
|
|
The interpreter is about to execute a new line of code or re-execute the
|
|
condition of a loop. The local trace function is called; *arg* is
|
|
``None``; the return value specifies the new local trace function. See
|
|
:file:`Objects/lnotab_notes.txt` for a detailed explanation of how this
|
|
works.
|
|
|
|
``'return'``
|
|
A function (or other code block) is about to return. The local trace
|
|
function is called; *arg* is the value that will be returned, or ``None``
|
|
if the event is caused by an exception being raised. The trace function's
|
|
return value is ignored.
|
|
|
|
``'exception'``
|
|
An exception has occurred. The local trace function is called; *arg* is a
|
|
tuple ``(exception, value, traceback)``; the return value specifies the
|
|
new local trace function.
|
|
|
|
``'c_call'``
|
|
A C function is about to be called. This may be an extension function or
|
|
a built-in. *arg* is the C function object.
|
|
|
|
``'c_return'``
|
|
A C function has returned. *arg* is the C function object.
|
|
|
|
``'c_exception'``
|
|
A C function has raised an exception. *arg* is the C function object.
|
|
|
|
Note that as an exception is propagated down the chain of callers, an
|
|
``'exception'`` event is generated at each level.
|
|
|
|
For more information on code and frame objects, refer to :ref:`types`.
|
|
|
|
.. impl-detail::
|
|
|
|
The :func:`settrace` function is intended only for implementing debuggers,
|
|
profilers, coverage tools and the like. Its behavior is part of the
|
|
implementation platform, rather than part of the language definition, and
|
|
thus may not be available in all Python implementations.
|
|
|
|
|
|
.. function:: settscdump(on_flag)
|
|
|
|
Activate dumping of VM measurements using the Pentium timestamp counter, if
|
|
*on_flag* is true. Deactivate these dumps if *on_flag* is off. The function is
|
|
available only if Python was compiled with ``--with-tsc``. To understand
|
|
the output of this dump, read :file:`Python/ceval.c` in the Python sources.
|
|
|
|
.. impl-detail::
|
|
This function is intimately bound to CPython implementation details and
|
|
thus not likely to be implemented elsewhere.
|
|
|
|
|
|
.. data:: stdin
|
|
stdout
|
|
stderr
|
|
|
|
:term:`File objects <file object>` used by the interpreter for standard
|
|
input, output and errors:
|
|
|
|
* ``stdin`` is used for all interactive input (including calls to
|
|
:func:`input`);
|
|
* ``stdout`` is used for the output of :func:`print` and :term:`expression`
|
|
statements and for the prompts of :func:`input`;
|
|
* The interpreter's own prompts and its error messages go to ``stderr``.
|
|
|
|
By default, these streams are regular text streams as returned by the
|
|
:func:`open` function. Their parameters are chosen as follows:
|
|
|
|
* The character encoding is platform-dependent. Under Windows, if the stream
|
|
is interactive (that is, if its :meth:`isatty` method returns True), the
|
|
console codepage is used, otherwise the ANSI code page. Under other
|
|
platforms, the locale encoding is used (see :meth:`locale.getpreferredencoding`).
|
|
|
|
Under all platforms though, you can override this value by setting the
|
|
:envvar:`PYTHONIOENCODING` environment variable.
|
|
|
|
* When interactive, standard streams are line-buffered. Otherwise, they
|
|
are block-buffered like regular text files. You can override this
|
|
value with the :option:`-u` command-line option.
|
|
|
|
To write or read binary data from/to the standard streams, use the
|
|
underlying binary :data:`~io.TextIOBase.buffer`. For example, to write
|
|
bytes to :data:`stdout`, use ``sys.stdout.buffer.write(b'abc')``. Using
|
|
:meth:`io.TextIOBase.detach`, streams can be made binary by default. This
|
|
function sets :data:`stdin` and :data:`stdout` to binary::
|
|
|
|
def make_streams_binary():
|
|
sys.stdin = sys.stdin.detach()
|
|
sys.stdout = sys.stdout.detach()
|
|
|
|
Note that the streams may be replaced with objects (like :class:`io.StringIO`)
|
|
that do not support the :attr:`~io.BufferedIOBase.buffer` attribute or the
|
|
:meth:`~io.BufferedIOBase.detach` method and can raise :exc:`AttributeError`
|
|
or :exc:`io.UnsupportedOperation`.
|
|
|
|
|
|
.. data:: __stdin__
|
|
__stdout__
|
|
__stderr__
|
|
|
|
These objects contain the original values of ``stdin``, ``stderr`` and
|
|
``stdout`` at the start of the program. They are used during finalization,
|
|
and could be useful to print to the actual standard stream no matter if the
|
|
``sys.std*`` object has been redirected.
|
|
|
|
It can also be used to restore the actual files to known working file objects
|
|
in case they have been overwritten with a broken object. However, the
|
|
preferred way to do this is to explicitly save the previous stream before
|
|
replacing it, and restore the saved object.
|
|
|
|
.. note::
|
|
Under some conditions ``stdin``, ``stdout`` and ``stderr`` as well as the
|
|
original values ``__stdin__``, ``__stdout__`` and ``__stderr__`` can be
|
|
None. It is usually the case for Windows GUI apps that aren't connected
|
|
to a console and Python apps started with :program:`pythonw`.
|
|
|
|
|
|
.. data:: thread_info
|
|
|
|
A :term:`struct sequence` holding information about the thread
|
|
implementation.
|
|
|
|
+------------------+---------------------------------------------------------+
|
|
| Attribute | Explanation |
|
|
+==================+=========================================================+
|
|
| :const:`name` | Name of the thread implementation: |
|
|
| | |
|
|
| | * ``'nt'``: Windows threads |
|
|
| | * ``'os2'``: OS/2 threads |
|
|
| | * ``'pthread'``: POSIX threads |
|
|
| | * ``'solaris'``: Solaris threads |
|
|
+------------------+---------------------------------------------------------+
|
|
| :const:`lock` | Name of the lock implementation: |
|
|
| | |
|
|
| | * ``'semaphore'``: a lock uses a semaphore |
|
|
| | * ``'mutex+cond'``: a lock uses a mutex |
|
|
| | and a condition variable |
|
|
| | * ``None`` if this information is unknown |
|
|
+------------------+---------------------------------------------------------+
|
|
| :const:`version` | Name and version of the thread library. It is a string, |
|
|
| | or ``None`` if these informations are unknown. |
|
|
+------------------+---------------------------------------------------------+
|
|
|
|
.. versionadded:: 3.3
|
|
|
|
|
|
.. data:: tracebacklimit
|
|
|
|
When this variable is set to an integer value, it determines the maximum number
|
|
of levels of traceback information printed when an unhandled exception occurs.
|
|
The default is ``1000``. When set to ``0`` or less, all traceback information
|
|
is suppressed and only the exception type and value are printed.
|
|
|
|
|
|
.. data:: version
|
|
|
|
A string containing the version number of the Python interpreter plus additional
|
|
information on the build number and compiler used. This string is displayed
|
|
when the interactive interpreter is started. Do not extract version information
|
|
out of it, rather, use :data:`version_info` and the functions provided by the
|
|
:mod:`platform` module.
|
|
|
|
|
|
.. data:: api_version
|
|
|
|
The C API version for this interpreter. Programmers may find this useful when
|
|
debugging version conflicts between Python and extension modules.
|
|
|
|
|
|
.. data:: version_info
|
|
|
|
A tuple containing the five components of the version number: *major*, *minor*,
|
|
*micro*, *releaselevel*, and *serial*. All values except *releaselevel* are
|
|
integers; the release level is ``'alpha'``, ``'beta'``, ``'candidate'``, or
|
|
``'final'``. The ``version_info`` value corresponding to the Python version 2.0
|
|
is ``(2, 0, 0, 'final', 0)``. The components can also be accessed by name,
|
|
so ``sys.version_info[0]`` is equivalent to ``sys.version_info.major``
|
|
and so on.
|
|
|
|
.. versionchanged:: 3.1
|
|
Added named component attributes.
|
|
|
|
.. data:: warnoptions
|
|
|
|
This is an implementation detail of the warnings framework; do not modify this
|
|
value. Refer to the :mod:`warnings` module for more information on the warnings
|
|
framework.
|
|
|
|
|
|
.. data:: winver
|
|
|
|
The version number used to form registry keys on Windows platforms. This is
|
|
stored as string resource 1000 in the Python DLL. The value is normally the
|
|
first three characters of :const:`version`. It is provided in the :mod:`sys`
|
|
module for informational purposes; modifying this value has no effect on the
|
|
registry keys used by Python. Availability: Windows.
|
|
|
|
|
|
.. data:: _xoptions
|
|
|
|
A dictionary of the various implementation-specific flags passed through
|
|
the :option:`-X` command-line option. Option names are either mapped to
|
|
their values, if given explicitly, or to :const:`True`. Example::
|
|
|
|
$ ./python -Xa=b -Xc
|
|
Python 3.2a3+ (py3k, Oct 16 2010, 20:14:50)
|
|
[GCC 4.4.3] on linux2
|
|
Type "help", "copyright", "credits" or "license" for more information.
|
|
>>> import sys
|
|
>>> sys._xoptions
|
|
{'a': 'b', 'c': True}
|
|
|
|
.. impl-detail::
|
|
|
|
This is a CPython-specific way of accessing options passed through
|
|
:option:`-X`. Other implementations may export them through other
|
|
means, or not at all.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
|
|
.. rubric:: Citations
|
|
|
|
.. [C99] ISO/IEC 9899:1999. "Programming languages -- C." A public draft of this standard is available at http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf .
|
|
|