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:mod:`sysconfig` --- Provide access to Python's configuration information

.. module:: sysconfig
   :synopsis: Python's configuration information


.. moduleauthor:: Tarek Ziadé <tarek@ziade.org>

.. sectionauthor:: Tarek Ziadé <tarek@ziade.org>


.. versionadded:: 3.2

Source code: :source:`Lib/sysconfig.py`

.. index::
   single: configuration information

The :mod:`sysconfig` module provides access to Python's configuration information like the list of installation paths and the configuration variables relevant for the current platform.

Configuration variables

A Python distribution contains a :file:`Makefile` and a :file:`pyconfig.h` header file that are necessary to build both the Python binary itself and third-party C extensions compiled using :mod:`distutils`.

:mod:`sysconfig` puts all variables found in these files in a dictionary that can be accessed using :func:`get_config_vars` or :func:`get_config_var`.

Notice that on Windows, it's a much smaller set.

.. function:: get_config_vars(\*args)

   With no arguments, return a dictionary of all configuration variables
   relevant for the current platform.

   With arguments, return a list of values that result from looking up each
   argument in the configuration variable dictionary.

   For each argument, if the value is not found, return ``None``.



.. function:: get_config_var(name)

   Return the value of a single variable *name*. Equivalent to
   ``get_config_vars().get(name)``.

   If *name* is not found, return ``None``.

Example of usage:

>>> import sysconfig
>>> sysconfig.get_config_var('Py_ENABLE_SHARED')
0
>>> sysconfig.get_config_var('LIBDIR')
'/usr/local/lib'
>>> sysconfig.get_config_vars('AR', 'CXX')
['ar', 'g++']

Installation paths

Python uses an installation scheme that differs depending on the platform and on the installation options. These schemes are stored in :mod:`sysconfig` under unique identifiers based on the value returned by :const:`os.name`.

Every new component that is installed using :mod:`distutils` or a Distutils-based system will follow the same scheme to copy its file in the right places.

Python currently supports seven schemes:

  • posix_prefix: scheme for Posix platforms like Linux or Mac OS X. This is the default scheme used when Python or a component is installed.
  • posix_home: scheme for Posix platforms used when a home option is used upon installation. This scheme is used when a component is installed through Distutils with a specific home prefix.
  • posix_user: scheme for Posix platforms used when a component is installed through Distutils and the user option is used. This scheme defines paths located under the user home directory.
  • nt: scheme for NT platforms like Windows.
  • nt_user: scheme for NT platforms, when the user option is used.

Each scheme is itself composed of a series of paths and each path has a unique identifier. Python currently uses eight paths:

  • stdlib: directory containing the standard Python library files that are not platform-specific.
  • platstdlib: directory containing the standard Python library files that are platform-specific.
  • platlib: directory for site-specific, platform-specific files.
  • purelib: directory for site-specific, non-platform-specific files.
  • include: directory for non-platform-specific header files.
  • platinclude: directory for platform-specific header files.
  • scripts: directory for script files.
  • data: directory for data files.

:mod:`sysconfig` provides some functions to determine these paths.

.. function:: get_scheme_names()

   Return a tuple containing all schemes currently supported in
   :mod:`sysconfig`.



.. function:: get_path_names()

   Return a tuple containing all path names currently supported in
   :mod:`sysconfig`.



.. function:: get_path(name, [scheme, [vars, [expand]]])

   Return an installation path corresponding to the path *name*, from the
   install scheme named *scheme*.

   *name* has to be a value from the list returned by :func:`get_path_names`.

   :mod:`sysconfig` stores installation paths corresponding to each path name,
   for each platform, with variables to be expanded.  For instance the *stdlib*
   path for the *nt* scheme is: ``{base}/Lib``.

   :func:`get_path` will use the variables returned by :func:`get_config_vars`
   to expand the path.  All variables have default values for each platform so
   one may call this function and get the default value.

   If *scheme* is provided, it must be a value from the list returned by
   :func:`get_scheme_names`.  Otherwise, the default scheme for the current
   platform is used.

   If *vars* is provided, it must be a dictionary of variables that will update
   the dictionary return by :func:`get_config_vars`.

   If *expand* is set to ``False``, the path will not be expanded using the
   variables.

   If *name* is not found, return ``None``.



.. function:: get_paths([scheme, [vars, [expand]]])

   Return a dictionary containing all installation paths corresponding to an
   installation scheme. See :func:`get_path` for more information.

   If *scheme* is not provided, will use the default scheme for the current
   platform.

   If *vars* is provided, it must be a dictionary of variables that will
   update the dictionary used to expand the paths.

   If *expand* is set to false, the paths will not be expanded.

   If *scheme* is not an existing scheme, :func:`get_paths` will raise a
   :exc:`KeyError`.

Other functions

.. function:: get_python_version()

   Return the ``MAJOR.MINOR`` Python version number as a string.  Similar to
   ``sys.version[:3]``.



.. function:: get_platform()

   Return a string that identifies the current platform.

   This is used mainly to distinguish platform-specific build directories and
   platform-specific built distributions.  Typically includes the OS name and
   version and the architecture (as supplied by :func:`os.uname`), although the
   exact information included depends on the OS; e.g. for IRIX the architecture
   isn't particularly important (IRIX only runs on SGI hardware), but for Linux
   the kernel version isn't particularly important.

   Examples of returned values:

   - linux-i586
   - linux-alpha (?)
   - solaris-2.6-sun4u
   - irix-5.3
   - irix64-6.2

   Windows will return one of:

   - win-amd64 (64bit Windows on AMD64 (aka x86_64, Intel64, EM64T, etc)
   - win-ia64 (64bit Windows on Itanium)
   - win32 (all others - specifically, sys.platform is returned)

   Mac OS X can return:

   - macosx-10.6-ppc
   - macosx-10.4-ppc64
   - macosx-10.3-i386
   - macosx-10.4-fat

   For other non-POSIX platforms, currently just returns :data:`sys.platform`.



.. function:: is_python_build()

   Return ``True`` if the running Python interpreter was built from source and
   is being run from its built location, and not from a location resulting from
   e.g. running ``make install`` or installing via a binary installer.



.. function:: parse_config_h(fp[, vars])

   Parse a :file:`config.h`\-style file.

   *fp* is a file-like object pointing to the :file:`config.h`\-like file.

   A dictionary containing name/value pairs is returned.  If an optional
   dictionary is passed in as the second argument, it is used instead of a new
   dictionary, and updated with the values read in the file.



.. function:: get_config_h_filename()

   Return the path of :file:`pyconfig.h`.


.. function:: get_makefile_filename()

   Return the path of :file:`Makefile`.

Using :mod:`sysconfig` as a script

You can use :mod:`sysconfig` as a script with Python's -m option:

$ python -m sysconfig
Platform: "macosx-10.4-i386"
Python version: "3.2"
Current installation scheme: "posix_prefix"

Paths:
        data = "/usr/local"
        include = "/Users/tarek/Dev/svn.python.org/py3k/Include"
        platinclude = "."
        platlib = "/usr/local/lib/python3.2/site-packages"
        platstdlib = "/usr/local/lib/python3.2"
        purelib = "/usr/local/lib/python3.2/site-packages"
        scripts = "/usr/local/bin"
        stdlib = "/usr/local/lib/python3.2"

Variables:
        AC_APPLE_UNIVERSAL_BUILD = "0"
        AIX_GENUINE_CPLUSPLUS = "0"
        AR = "ar"
        ARFLAGS = "rc"
        ASDLGEN = "./Parser/asdl_c.py"
        ...

This call will print in the standard output the information returned by :func:`get_platform`, :func:`get_python_version`, :func:`get_path` and :func:`get_config_vars`.