1:mod:`sysconfig` --- Provide access to Python's configuration information
2=========================================================================
3
4.. module:: sysconfig
5   :synopsis: Python's configuration information
6
7.. moduleauthor:: Tarek Ziadé <tarek@ziade.org>
8.. sectionauthor:: Tarek Ziadé <tarek@ziade.org>
9
10.. versionadded:: 3.2
11
12**Source code:** :source:`Lib/sysconfig.py`
13
14.. index::
15   single: configuration information
16
17--------------
18
19The :mod:`sysconfig` module provides access to Python's configuration
20information like the list of installation paths and the configuration variables
21relevant for the current platform.
22
23Configuration variables
24-----------------------
25
26A Python distribution contains a :file:`Makefile` and a :file:`pyconfig.h`
27header file that are necessary to build both the Python binary itself and
28third-party C extensions compiled using :mod:`distutils`.
29
30:mod:`sysconfig` puts all variables found in these files in a dictionary that
31can be accessed using :func:`get_config_vars` or :func:`get_config_var`.
32
33Notice that on Windows, it's a much smaller set.
34
35.. function:: get_config_vars(*args)
36
37   With no arguments, return a dictionary of all configuration variables
38   relevant for the current platform.
39
40   With arguments, return a list of values that result from looking up each
41   argument in the configuration variable dictionary.
42
43   For each argument, if the value is not found, return ``None``.
44
45
46.. function:: get_config_var(name)
47
48   Return the value of a single variable *name*. Equivalent to
49   ``get_config_vars().get(name)``.
50
51   If *name* is not found, return ``None``.
52
53Example of usage::
54
55   >>> import sysconfig
56   >>> sysconfig.get_config_var('Py_ENABLE_SHARED')
57   0
58   >>> sysconfig.get_config_var('LIBDIR')
59   '/usr/local/lib'
60   >>> sysconfig.get_config_vars('AR', 'CXX')
61   ['ar', 'g++']
62
63
64Installation paths
65------------------
66
67Python uses an installation scheme that differs depending on the platform and on
68the installation options.  These schemes are stored in :mod:`sysconfig` under
69unique identifiers based on the value returned by :const:`os.name`.
70
71Every new component that is installed using :mod:`distutils` or a
72Distutils-based system will follow the same scheme to copy its file in the right
73places.
74
75Python currently supports seven schemes:
76
77- *posix_prefix*: scheme for POSIX platforms like Linux or Mac OS X.  This is
78  the default scheme used when Python or a component is installed.
79- *posix_home*: scheme for POSIX platforms used when a *home* option is used
80  upon installation.  This scheme is used when a component is installed through
81  Distutils with a specific home prefix.
82- *posix_user*: scheme for POSIX platforms used when a component is installed
83  through Distutils and the *user* option is used.  This scheme defines paths
84  located under the user home directory.
85- *nt*: scheme for NT platforms like Windows.
86- *nt_user*: scheme for NT platforms, when the *user* option is used.
87
88Each scheme is itself composed of a series of paths and each path has a unique
89identifier.  Python currently uses eight paths:
90
91- *stdlib*: directory containing the standard Python library files that are not
92  platform-specific.
93- *platstdlib*: directory containing the standard Python library files that are
94  platform-specific.
95- *platlib*: directory for site-specific, platform-specific files.
96- *purelib*: directory for site-specific, non-platform-specific files.
97- *include*: directory for non-platform-specific header files.
98- *platinclude*: directory for platform-specific header files.
99- *scripts*: directory for script files.
100- *data*: directory for data files.
101
102:mod:`sysconfig` provides some functions to determine these paths.
103
104.. function:: get_scheme_names()
105
106   Return a tuple containing all schemes currently supported in
107   :mod:`sysconfig`.
108
109
110.. function:: get_path_names()
111
112   Return a tuple containing all path names currently supported in
113   :mod:`sysconfig`.
114
115
116.. function:: get_path(name, [scheme, [vars, [expand]]])
117
118   Return an installation path corresponding to the path *name*, from the
119   install scheme named *scheme*.
120
121   *name* has to be a value from the list returned by :func:`get_path_names`.
122
123   :mod:`sysconfig` stores installation paths corresponding to each path name,
124   for each platform, with variables to be expanded.  For instance the *stdlib*
125   path for the *nt* scheme is: ``{base}/Lib``.
126
127   :func:`get_path` will use the variables returned by :func:`get_config_vars`
128   to expand the path.  All variables have default values for each platform so
129   one may call this function and get the default value.
130
131   If *scheme* is provided, it must be a value from the list returned by
132   :func:`get_scheme_names`.  Otherwise, the default scheme for the current
133   platform is used.
134
135   If *vars* is provided, it must be a dictionary of variables that will update
136   the dictionary return by :func:`get_config_vars`.
137
138   If *expand* is set to ``False``, the path will not be expanded using the
139   variables.
140
141   If *name* is not found, return ``None``.
142
143
144.. function:: get_paths([scheme, [vars, [expand]]])
145
146   Return a dictionary containing all installation paths corresponding to an
147   installation scheme. See :func:`get_path` for more information.
148
149   If *scheme* is not provided, will use the default scheme for the current
150   platform.
151
152   If *vars* is provided, it must be a dictionary of variables that will
153   update the dictionary used to expand the paths.
154
155   If *expand* is set to false, the paths will not be expanded.
156
157   If *scheme* is not an existing scheme, :func:`get_paths` will raise a
158   :exc:`KeyError`.
159
160
161Other functions
162---------------
163
164.. function:: get_python_version()
165
166   Return the ``MAJOR.MINOR`` Python version number as a string.  Similar to
167   ``'%d.%d' % sys.version_info[:2]``.
168
169
170.. function:: get_platform()
171
172   Return a string that identifies the current platform.
173
174   This is used mainly to distinguish platform-specific build directories and
175   platform-specific built distributions.  Typically includes the OS name and
176   version and the architecture (as supplied by 'os.uname()'), although the
177   exact information included depends on the OS; e.g., on Linux, the kernel
178   version isn't particularly important.
179
180   Examples of returned values:
181
182   - linux-i586
183   - linux-alpha (?)
184   - solaris-2.6-sun4u
185
186   Windows will return one of:
187
188   - win-amd64 (64bit Windows on AMD64, aka x86_64, Intel64, and EM64T)
189   - win32 (all others - specifically, sys.platform is returned)
190
191   Mac OS X can return:
192
193   - macosx-10.6-ppc
194   - macosx-10.4-ppc64
195   - macosx-10.3-i386
196   - macosx-10.4-fat
197
198   For other non-POSIX platforms, currently just returns :data:`sys.platform`.
199
200
201.. function:: is_python_build()
202
203   Return ``True`` if the running Python interpreter was built from source and
204   is being run from its built location, and not from a location resulting from
205   e.g. running ``make install`` or installing via a binary installer.
206
207
208.. function:: parse_config_h(fp[, vars])
209
210   Parse a :file:`config.h`\-style file.
211
212   *fp* is a file-like object pointing to the :file:`config.h`\-like file.
213
214   A dictionary containing name/value pairs is returned.  If an optional
215   dictionary is passed in as the second argument, it is used instead of a new
216   dictionary, and updated with the values read in the file.
217
218
219.. function:: get_config_h_filename()
220
221   Return the path of :file:`pyconfig.h`.
222
223.. function:: get_makefile_filename()
224
225   Return the path of :file:`Makefile`.
226
227Using :mod:`sysconfig` as a script
228----------------------------------
229
230You can use :mod:`sysconfig` as a script with Python's *-m* option:
231
232.. code-block:: shell-session
233
234    $ python -m sysconfig
235    Platform: "macosx-10.4-i386"
236    Python version: "3.2"
237    Current installation scheme: "posix_prefix"
238
239    Paths:
240            data = "/usr/local"
241            include = "/Users/tarek/Dev/svn.python.org/py3k/Include"
242            platinclude = "."
243            platlib = "/usr/local/lib/python3.2/site-packages"
244            platstdlib = "/usr/local/lib/python3.2"
245            purelib = "/usr/local/lib/python3.2/site-packages"
246            scripts = "/usr/local/bin"
247            stdlib = "/usr/local/lib/python3.2"
248
249    Variables:
250            AC_APPLE_UNIVERSAL_BUILD = "0"
251            AIX_GENUINE_CPLUSPLUS = "0"
252            AR = "ar"
253            ARFLAGS = "rc"
254            ...
255
256This call will print in the standard output the information returned by
257:func:`get_platform`, :func:`get_python_version`, :func:`get_path` and
258:func:`get_config_vars`.
259