Source code:
Lib/site.py
This module is automatically imported during initialization.
The automatic
import can be suppressed using the interpreter’s
-S
option.
Importing this module normally appends site-specific paths to the module search path
and adds
callables
, including
help()
to the built-in
namespace. However, Python startup 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
main()
function.
Changed in version 3.3:
Importing the module used to trigger paths manipulation even when using
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
lib/site-packages
(on Windows) or
lib/python
X.Y[t]
/site-packages
(on Unix and macOS). (The
optional suffix “t” indicates the
free threading
build, and is
appended if
"t"
is present in the
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.
Changed in version 3.5:
Support for the “site-python” directory has been removed.
Changed in version 3.13:
On Unix,
Free threading
Python installations are
identified by the “t” suffix in the version-specific directory name, such as
lib/python3.13t/
.
If a file named “pyvenv.cfg” exists one directory above sys.executable,
sys.prefix and sys.exec_prefix are set to that directory and
it is also checked for site-packages (sys.base_prefix and
sys.base_exec_prefix will always be the “real” prefixes of the Python
installation). If “pyvenv.cfg” (a bootstrap configuration file) contains
the key “include-system-site-packages” set to anything other than “true”
(case-insensitive), the system-level prefixes will not be
searched for site-packages; otherwise they will.
A path configuration file is a file whose name has the form
name
.pth
and exists in one of the four directories mentioned above; its contents are
additional items (one per line) to be added to
sys.path
. Non-existing items
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. Lines starting
with
import
(followed by space or tab) are executed.
An executable line in a
.pth
file is run at every Python startup,
regardless of whether a particular module is actually going to be used.
Its impact should thus be kept to a minimum.
The primary intended purpose of executable lines is to make the
corresponding module(s) importable
(load 3rd-party import hooks, adjust
PATH
etc).
Any other initialization is supposed to be done upon a module’s
actual import, if and when it happens.
Limiting a code chunk to a single line is a deliberate measure
to discourage putting anything more complex here.
Changed in version 3.13:
The
.pth
files are now decoded by UTF-8 at first and then by the
locale encoding
if it fails.
For example, suppose
sys.prefix
and
sys.exec_prefix
are set to
/usr/local
. The Python X.Y library is then installed in
/usr/local/lib/python
X.Y
. Suppose this has
a subdirectory
/usr/local/lib/python
X.Y
/site-packages
with three
subsubdirectories,
foo
,
bar
and
spam
, and two path
configuration files,
foo.pth
and
bar.pth
. Assume
foo.pth
contains the following:
# foo package configuration
bletch
and bar.pth contains:
# bar package configuration
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 bletch is omitted because it doesn’t exist; the bar
directory precedes the foo directory because bar.pth comes
alphabetically before foo.pth; and spam is omitted because it is
not mentioned in either path configuration file.
After these path manipulations, an attempt is made to import a module named
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 ImportError or its subclass
exception, and the exception’s name
attribute equals to 'sitecustomize',
it is silently ignored. If Python is started without output streams available, as
with pythonw.exe on Windows (which is used by default to start IDLE),
attempted output from sitecustomize is ignored. Any other exception
causes a silent and perhaps mysterious failure of the process.
After this, an attempt is made to import a module named usercustomize,
which can perform arbitrary user-specific customizations, if
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 -s. If this import fails with an ImportError or
its subclass exception, and the exception’s name
attribute equals to '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
sitecustomize and usercustomize is still attempted.
Readline configuration
On systems that support readline, this module will also import and
configure the rlcompleter module, if Python is started in
interactive mode and without the -S option.
The default behavior is enable tab-completion and to use
~/.python_history as the history save file. To disable it, delete (or
override) the sys.__interactivehook__ attribute in your
sitecustomize or usercustomize module or your
PYTHONSTARTUP file.
Changed in version 3.4: Activation of rlcompleter and history was made automatic.
Module contents
site.PREFIXES
A list of prefixes for site-packages directories.
site.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 -s or
PYTHONNOUSERSITE). None means it was disabled for security
reasons (mismatch between user or group id and effective id) or by an
administrator.
site.USER_SITE
Path to the user site-packages for the running Python. Can be None if
getusersitepackages() hasn’t been called yet. Default value is
~/.local/lib/pythonX.Y[t]/site-packages for UNIX and non-framework
macOS builds, ~/Library/Python/X.Y/lib/python/site-packages for macOS
framework builds, and %APPDATA%\Python\PythonXY\site-packages
on Windows. The optional “t” indicates the free-threaded build. This
directory is a site directory, which means that .pth files in it
will be processed.
site.USER_BASE
Path to the base directory for the user site-packages. Can be None if
getuserbase() hasn’t been called yet. Default value is
~/.local for UNIX and macOS non-framework builds,
~/Library/Python/X.Y for macOS framework builds, and
%APPDATA%\Python for Windows. This value is used to
compute the installation directories for scripts, data files, Python modules,
etc. for the user installation scheme.
See also PYTHONUSERBASE.
site.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 -S flag.
Changed in version 3.3: This function used to be called unconditionally.
site.addsitedir(sitedir, known_paths=None)
Add a directory to sys.path and process its .pth files. Typically
used in sitecustomize or usercustomize (see above).
site.getsitepackages()
Return a list containing all global site-packages directories.
Added in version 3.2.
site.getuserbase()
Return the path of the user base directory, USER_BASE. If it is not
initialized yet, this function will also set it, respecting
PYTHONUSERBASE.
Added in version 3.2.
site.getusersitepackages()
Return the path of the user-specific site-packages directory,
USER_SITE. If it is not initialized yet, this function will also set
it, respecting USER_BASE. To determine if the user-specific
site-packages was added to sys.path ENABLE_USER_SITE should be
used.
Added in version 3.2.
Command Line Interface
The site module also provides a way to get the user directories from the
command line:
$ 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
sys.path on the standard output, followed by the value of
USER_BASE and whether the directory exists, then the same thing for
USER_SITE, and finally the value of ENABLE_USER_SITE.
--user-base
Print the path to the user base directory.
If both options are given, user base and user site will be printed (always in
this order), separated by 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.
See also
PEP 370 – Per user site-packages directory
The initialization of the sys.path module search path – The initialization of sys.path.
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