29.2. "sysconfig" --- Provide access to Python's configuration information
**************************************************************************

3.2 新版功能.

**源代码：** Lib/sysconfig.py

======================================================================

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


29.2.1. 配置变量
================

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

"sysconfig" puts all variables found in these files in a dictionary
that can be accessed using "get_config_vars()" or "get_config_var()".

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

sysconfig.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".

sysconfig.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".

用法示例:

   >>> 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++']


29.2.2. 安装路径
================

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

Every new component that is installed using "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.

"sysconfig" provides some functions to determine these paths.

sysconfig.get_scheme_names()

   Return a tuple containing all schemes currently supported in
   "sysconfig".

sysconfig.get_path_names()

   Return a tuple containing all path names currently supported in
   "sysconfig".

sysconfig.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
   "get_path_names()".

   "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".

   "get_path()" will use the variables returned by "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 "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 "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".

sysconfig.get_paths([scheme[, vars[, expand]]])

   Return a dictionary containing all installation paths corresponding
   to an installation scheme. See "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, "get_paths()" will raise a
   "KeyError".


29.2.3. 其他功能
================

sysconfig.get_python_version()

   Return the "MAJOR.MINOR" Python version number as a string.
   Similar to "'%d.%d' % sys.version_info[:2]".

sysconfig.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 "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.

   返回值的示例：

   * linux-i586

   * linux-alpha (?)

   * solaris-2.6-sun4u

   * irix-5.3

   * irix64-6.2

   Windows将返回以下之一：

   * win-amd64 (在 AMD64, aka x86_64, Intel64, 和 EM64T上的64位
     Windows )

   * win-ia64 (64bit Windows on Itanium)

   * win32 (all others - specifically, sys.platform is returned)

   Mac OS X 返回：

   * macosx-10.6-ppc

   * macosx-10.4-ppc64

   * macosx-10.3-i386

   * macosx-10.4-fat

   对于其他非-POSIX 平台， 目前只是返回 "sys.platform" 。

sysconfig.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.

sysconfig.parse_config_h(fp[, vars])

   Parse a "config.h"-style file.

   *fp* is a file-like object pointing to the "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.

sysconfig.get_config_h_filename()

   返回  "pyconfig.h" 的目录

sysconfig.get_makefile_filename()

   返回 "Makefile" 的目录


29.2.4. Using "sysconfig" as a script
=====================================

You can use "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"
           ...

This call will print in the standard output the information returned
by "get_platform()", "get_python_version()", "get_path()" and
"get_config_vars()".
