Doc/library/site.rst
!site --- Site-specific configuration hook.. module:: site :synopsis: Module responsible for site-specific configuration.
Source code: :source:Lib/site.py
.. highlight:: none
This module is automatically imported during initialization. The automatic
import can be suppressed using the interpreter's :option:-S option.
.. index:: triple: module; search; path
Importing this module normally appends site-specific paths to the module search path
and adds :ref:callables <site-consts>, including :func:help to the built-in
namespace. However, Python startup option :option:-S blocks this, and this module
can be safely imported with no automatic modifications to the module search path
or additions to the builtins. To explicitly trigger the usual site-specific
additions, call the :func:main function.
.. versionchanged:: 3.3
Importing the module used to trigger paths manipulation even when using
:option:-S.
.. index:: pair: site-packages; directory
It starts by constructing up to four directories from a head and a tail part.
For the head part, it uses sys.prefix and sys.exec_prefix; empty heads
are skipped. For the tail part, it uses the empty string and then
:file:lib/site-packages (on Windows) or
:file:lib/python{X.Y[t]}/site-packages (on Unix and macOS). (The
optional suffix "t" indicates the :term:free-threaded build, and is
appended if "t" is present in the :data:sys.abiflags constant.)
For each
of the distinct head-tail combinations, it sees if it refers to an existing
directory, and if so, adds it to sys.path and also inspects the newly
added path for configuration files.
.. versionchanged:: 3.5 Support for the "site-python" directory has been removed.
.. versionchanged:: 3.13
On Unix, :term:Free threading <free threading> Python installations are
identified by the "t" suffix in the version-specific directory name, such as
:file:lib/python3.13t/.
.. versionchanged:: 3.14
:mod:!site is no longer responsible for updating :data:sys.prefix and
:data:sys.exec_prefix on :ref:sys-path-init-virtual-environments. This is
now done during the :ref:path initialization <sys-path-init>. As a result,
under :ref:sys-path-init-virtual-environments, :data:sys.prefix and
:data:sys.exec_prefix no longer depend on the :mod:!site initialization,
and are therefore unaffected by :option:-S.
.. _site-virtual-environments-configuration:
When running under a :ref:virtual environment <sys-path-init-virtual-environments>,
the pyvenv.cfg file in :data:sys.prefix is checked for site-specific
configurations. If the include-system-site-packages key exists and is set to
true (case-insensitive), the system-level prefixes will be searched for
site-packages, otherwise they won't. If the system-level prefixes are not searched then
the user site prefixes are also implicitly not searched for site-packages.
.. index:: single: # (hash); comment pair: statement; import
The :mod:!site module recognizes two startup configuration files of the form
:file:{name}.pth for path configurations, and :file:{name}.start for
pre-first-line code execution. Both files can exist in one of the four
directories mentioned above. Within each directory, these files are sorted
alphabetically by filename, then parsed in sorted order.
.. _site-pth-files:
.pth files):file:{name}.pth contains additional items (one per line) to be appended to
sys.path. Items that name non-existing directories are never added to
sys.path, and no check is made that the item refers to a directory rather
than a file. No item is added to sys.path more than once. Blank lines
and lines beginning with # are skipped.
For backward compatibility, lines starting with import (followed by space
or tab) are executed with :func:exec.
.. versionchanged:: 3.13
The :file:.pth files are now decoded by UTF-8 at first and then by the
:term:locale encoding if it fails.
.. versionchanged:: 3.15
:file:.pth file lines starting with import are deprecated. During
the deprecation period, such lines are still executed (except in the case
below), but a diagnostic message is emitted only when the :option:-v flag
is given.
import lines in :file:{name}.pth are silently ignored when a
:ref:matching <site-start-files> :file:{name}.start file exists.
Errors on individual lines no longer abort processing of the rest of the file. Each error is reported and the remaining lines continue to be processed.
.. deprecated-removed:: 3.15 3.20
Decoding :file:{name}.pth files in any encoding other than utf-8-sig
is deprecated in Python 3.15, and support for decoding from the locale
encoding will be removed in Python 3.20.
import lines in :file:{name}.pth files are deprecated and will be
silently ignored in Python 3.18 and 3.19. In Python 3.20 a warning will be
produced for import lines in :file:{name}.pth files.
.. _site-start-files:
.start files).. versionadded:: 3.15
A startup entry point file is a file whose name has the form
:file:{name}.start and exists in one of the site-packages directories
described above. Each file specifies entry points to be called during
interpreter startup, using the pkg.mod:callable syntax understood by
:func:pkgutil.resolve_name.
Each non-blank line that does not begin with # must contain an entry
point reference in the form pkg.mod:callable. The colon and callable
portion are mandatory. Each callable is invoked with no arguments, and
any return value is discarded.
:file:.start files are processed after all :file:.pth path extensions
have been applied to :data:sys.path, ensuring that paths are available
before any startup code runs.
Unlike :data:sys.path extensions from :file:.pth files, duplicate entry
points are not de-duplicated --- if an entry point appears more than once,
it will be called more than once.
If an exception occurs during resolution or invocation of an entry point,
a traceback is printed to :data:sys.stderr and processing continues with
the remaining entry points.
:file:.start files must be encoded in UTF-8.
:pep:829 defined the original specification for these features.
.. note::
If a :file:{name}.start file exists alongside a :file:{name}.pth file
with the same base name, any import lines in the :file:.pth file are
ignored in favor of the entry points in the :file:.start file.
.. note::
Executable lines (import lines in :file:{name}.pth files and
:file:{name}.start file entry points) are always run at Python startup
(unless :option:-S is given to disable the site.py module entirely),
regardless of whether a particular module is actually going to be used.
.. note::
:file:{name}.start files invoke :func:pkgutil.resolve_name with
strict=True, which requires the full pkg.mod:callable form.
.. index:: single: package triple: path; configuration; file
For example, suppose sys.prefix and sys.exec_prefix are set to
:file:/usr/local. The Python X.Y library is then installed in
:file:/usr/local/lib/python{X.Y}. Suppose this has
a subdirectory :file:/usr/local/lib/python{X.Y}/site-packages with three
sub-subdirectories, :file:foo, :file:bar and :file:spam, and two path
configuration files, :file:foo.pth and :file:bar.pth. Assume
:file:foo.pth contains the following::
foo bar bletch
and :file:bar.pth contains::
bar
Then the following version-specific directories are added to
sys.path, in this order::
/usr/local/lib/pythonX.Y/site-packages/bar /usr/local/lib/pythonX.Y/site-packages/foo
Note that :file:bletch is omitted because it doesn't exist; the :file:bar
directory precedes the :file:foo directory because :file:bar.pth comes
alphabetically before :file:foo.pth; and :file:spam is omitted because it is
not mentioned in either path configuration file.
Let's say that there is also a :file:foo.start file containing the
following::
# foo package startup code
foo.submod:initialize
Now, after sys.path has been extended as above, and before Python turns
control over to user code, the foo.submod module is imported and the
initialize() function from that module is called.
.. _site-migration-guide:
import lines in .pth files to .start filesIf your package currently ships a :file:{name}.pth file, you can keep all
sys.path extension lines unchanged. Only import lines need to be
migrated.
To migrate, create a callable (taking zero arguments) within an importable
module in your package. Reference it as a pkg.mod:callable entry point
in a matching :file:{name}.start file. Move everything on your import
line after the first semi-colon into the callable() function.
If your package must straddle older Pythons that do not support :pep:829
and newer Pythons that do, change the import lines in your
:file:{name}.pth to use the following form:
.. code-block:: python
import pkg.mod; pkg.mod.callable()
Older Pythons will execute these import lines, while newer Pythons will
ignore them in favor of the :file:{name}.start file. After the straddling
period, remove all import lines from your :file:.pth files.
!sitecustomize.. module:: sitecustomize
After these path manipulations, an attempt is made to import a module named
:mod:!sitecustomize, which can perform arbitrary site-specific customizations.
It is typically created by a system administrator in the site-packages
directory. If this import fails with an :exc:ImportError or its subclass
exception, and the exception's :attr:~ImportError.name
attribute equals 'sitecustomize',
it is silently ignored. If Python is started without output streams available, as
with :file:pythonw.exe on Windows (which is used by default to start IDLE),
attempted output from :mod:!sitecustomize is ignored. Any other exception
causes a silent and perhaps mysterious failure of the process.
!usercustomize.. module:: usercustomize
After this, an attempt is made to import a module named :mod:!usercustomize,
which can perform arbitrary user-specific customizations, if
:data:~site.ENABLE_USER_SITE is true. This file is intended to be created in the
user site-packages directory (see below), which is part of sys.path unless
disabled by :option:-s. If this import fails with an :exc:ImportError or
its subclass exception, and the exception's :attr:~ImportError.name
attribute equals 'usercustomize', it is silently ignored.
Note that for some non-Unix systems, sys.prefix and sys.exec_prefix are
empty, and the path manipulations are skipped; however the import of
:mod:sitecustomize and :mod:!usercustomize is still attempted.
.. currentmodule:: site
.. _rlcompleter-config:
On systems that support :mod:readline, this module will also import and
configure the :mod:rlcompleter module, if Python is started in
:ref:interactive mode <tut-interactive> and without the :option:-S option.
The default behavior is to enable tab completion and to use
:file:~/.python_history as the history save file. To disable it, delete (or
override) the :data:sys.__interactivehook__ attribute in your
:mod:sitecustomize or :mod:usercustomize module or your
:envvar:PYTHONSTARTUP file.
.. versionchanged:: 3.4 Activation of rlcompleter and history was made automatic.
.. data:: PREFIXES
A list of prefixes for site-packages directories.
.. data:: ENABLE_USER_SITE
Flag showing the status of the user site-packages directory. True means
that it is enabled and was added to sys.path. False means that it
was disabled by user request (with :option:-s or
:envvar:PYTHONNOUSERSITE). None means it was disabled for security
reasons (mismatch between user or group id and effective id) or by an
administrator.
.. data:: USER_SITE
Path to the user site-packages for the running Python. Can be None if
:func:getusersitepackages hasn't been called yet. Default value is
:file:~/.local/lib/python{X.Y}[t]/site-packages for UNIX and non-framework
macOS builds, :file:~/Library/Python/{X.Y}/lib/python/site-packages for macOS
framework builds, and :file:{%APPDATA%}\\Python\\Python{XY}\\site-packages
on Windows. The optional "t" indicates the free-threaded build. This
directory is a site directory, which means that :file:.pth files in it
will be processed.
.. data:: USER_BASE
Path to the base directory for the user site-packages. Can be None if
:func:getuserbase hasn't been called yet. Default value is
:file:~/.local for UNIX and macOS non-framework builds,
:file:~/Library/Python/{X.Y} for macOS framework builds, and
:file:{%APPDATA%}\\Python for Windows. This value is used to
compute the installation directories for scripts, data files, Python modules,
etc. for the :ref:user installation scheme <sysconfig-user-scheme>.
See also :envvar:PYTHONUSERBASE.
.. function:: main()
Adds all the standard site-specific directories to the module search
path. This function is called automatically when this module is imported,
unless the Python interpreter was started with the :option:-S flag.
.. versionchanged:: 3.3 This function used to be called unconditionally.
.. function:: addsitedir(sitedir, known_paths=None, *, defer_processing_start_files=False)
Add a directory to sys.path and parse the :file:.pth and :file:.start
files found in that directory. Typically used in :mod:sitecustomize or
:mod:usercustomize (see above).
The known_paths argument is an optional set of case-normalized paths
used to prevent duplicate :data:sys.path entries. When None (the
default), the set is built from the current :data:sys.path.
While :file:.pth and :file:.start files are always parsed, set
defer_processing_start_files to True to prevent processing the
startup data found in those files, so that you can process them explicitly
(this is typically used by the :func:main function).
.. versionchanged:: 3.15
Also processes :file:`.start` files. See :ref:`site-start-files`.
All :file:`.pth` and :file:`.start` files are now read and
accumulated before any path extensions, ``import`` line execution,
or entry point invocations take place.
.. function:: getsitepackages()
Return a list containing all global site-packages directories.
.. versionadded:: 3.2
.. function:: getuserbase()
Return the path of the user base directory, :data:USER_BASE. If it is not
initialized yet, this function will also set it, respecting
:envvar:PYTHONUSERBASE.
.. versionadded:: 3.2
.. function:: getusersitepackages()
Return the path of the user-specific site-packages directory,
:data:USER_SITE. If it is not initialized yet, this function will also set
it, respecting :data:USER_BASE. To determine if the user-specific
site-packages was added to sys.path :data:ENABLE_USER_SITE should be
used.
.. versionadded:: 3.2
.. _site-commandline:
.. program:: site
The :mod:!site module also provides a way to get the user directories from the
command line:
.. code-block:: shell-session
$ python -m site --user-site /home/user/.local/lib/python3.11/site-packages
If it is called without arguments, it will print the contents of
:data:sys.path on the standard output, followed by the value of
:data:USER_BASE and whether the directory exists, then the same thing for
:data:USER_SITE, and finally the value of :data:ENABLE_USER_SITE.
.. option:: --user-base
Print the path to the user base directory.
.. option:: --user-site
Print the path to the user site-packages directory.
If both options are given, user base and user site will be printed (always in
this order), separated by :data:os.pathsep.
If any option is given, the script will exit with one of these values: 0 if
the user site-packages directory is enabled, 1 if it was disabled by the
user, 2 if it is disabled for security reasons or by an administrator, and a
value greater than 2 if there is an error.
.. seealso::
370 -- Per user site-packages directory829 -- Startup entry points and the deprecation of import lines in .pth filessys-path-init -- The initialization of :data:sys.path.