site — Site-specific configuration hook

Código Fuente: Lib/site.py

Este módulo se importa automáticamente durante la inicialización. La importación automática se puede suprimir utilizando la opción del intérprete opción -S .

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.

Distinto en la versión 3.3: Importar el módulo utilizado para activar la manipulación de rutas incluso cuando se utiliza -S.

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/pythonX.Y[t]/site-packages (on Unix and macOS). (The optional suffix «t» indicates the free-threaded 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.

Distinto en la versión 3.5: Se ha eliminado la compatibilidad con el directorio «site-python».

Distinto en la versión 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/.

Distinto en la versión 3.14: site is no longer responsible for updating sys.prefix and sys.exec_prefix on Virtual Environments. This is now done during the path initialization. As a result, under Virtual Environments, sys.prefix and sys.exec_prefix no longer depend on the site initialization, and are therefore unaffected by -S.

When running under a virtual environment, the pyvenv.cfg file in 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.

The site module recognizes two startup configuration files of the form name.pth for path configurations, and 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.

Path extensions (.pth files)

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 exec().

Distinto en la versión 3.13: The .pth files are now decoded by UTF-8 at first and then by the locale encoding if it fails.

Distinto en la versión 3.15: .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 -v flag is given.

import lines in name.pth are silently ignored when a matching 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 since version 3.15, will be removed in version 3.20: Decoding 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 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 name.pth files.

Startup entry points (.start files)

Added in version 3.15.

A startup entry point file is a file whose name has the form 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 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.

.start files are processed after all .pth path extensions have been applied to sys.path, ensuring that paths are available before any startup code runs.

Unlike sys.path extensions from .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 sys.stderr and processing continues with the remaining entry points.

.start files must be encoded in UTF-8.

PEP 829 defined the original specification for these features.

Nota

If a name.start file exists alongside a name.pth file with the same base name, any import lines in the .pth file are ignored in favor of the entry points in the .start file.

Nota

Executable lines (import lines in name.pth files and name.start file entry points) are always run at Python startup (unless -S is given to disable the site.py module entirely), regardless of whether a particular module is actually going to be used.

Nota

name.start files invoke pkgutil.resolve_name() with strict=True, which requires the full pkg.mod:callable form.

Startup file examples

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/pythonX.Y. Suppose this has a subdirectory /usr/local/lib/pythonX.Y/site-packages with three sub-subdirectories, foo, bar and spam, and two path configuration files, foo.pth and bar.pth. Assume foo.pth contains the following:

# foo package configuration

foo
bar
bletch

y bar.pth contiene:

# bar package configuration

bar

Luego, los siguientes directorios específicos de la versión se agregan a sys.path, en este orden:

/usr/local/lib/pythonX.Y/site-packages/bar
/usr/local/lib/pythonX.Y/site-packages/foo

Tenga en cuenta que bletch se omite porque no existe; el directorio bar precede al directorio foo porque bar.pth viene alfabéticamente antes de foo.pth; y spam se omite porque no se menciona en ninguno de los archivos de configuración de ruta.

Let’s say that there is also a 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.

Migrating from import lines in .pth files to .start files

If your package currently ships a 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 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 name.pth to use the following form:

import pkg.mod; pkg.mod.callable()

Older Pythons will execute these import lines, while newer Pythons will ignore them in favor of the name.start file. After the straddling period, remove all import lines from your .pth files.

sitecustomize

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 '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.

usercustomize

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 '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.

Configuración de Readline

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 to 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.

Distinto en la versión 3.4: La activación de rlcompleter y el historial se hizo automática.

Contenido del módulo

site.PREFIXES

Una lista de prefijos para directorios de site-packages.

site.ENABLE_USER_SITE

Flag que muestra el estado del directorio site-packages del usuario. True significa que está habilitado y se agregó a sys.path. False significa que fue deshabilitado por solicitud del usuario (con -s o PYTHONNOUSERSITE). None significa que fue deshabilitado por razones de seguridad (falta de coincidencia entre la identificación de usuario o grupo y la identificación efectiva) o por un administrador.

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()

Agrega todos los directorios estándar específicos del sitio a la ruta de búsqueda del módulo. Esta función se llama automáticamente cuando se importa este módulo, a menos que el intérprete de Python se haya iniciado con la opción -S.

Distinto en la versión 3.3: Esta función solía llamarse incondicionalmente.

site.addsitedir(sitedir, known_paths=None, *, defer_processing_start_files=False)

Add a directory to sys.path and parse the .pth and .start files found in that directory. Typically used in sitecustomize or usercustomize (see above).

The known_paths argument is an optional set of case-normalized paths used to prevent duplicate sys.path entries. When None (the default), the set is built from the current sys.path.

While .pth and .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 main() function).

Distinto en la versión 3.15: Also processes .start files. See Startup entry points (.start files). All .pth and .start files are now read and accumulated before any path extensions, import line execution, or entry point invocations take place.

site.getsitepackages()

Retorna una lista que contiene todos los directorios site-packages globales.

Added in version 3.2.

site.getuserbase()

Retorna la ruta del directorio base del usuario USER_BASE. Si este aún no fue inicializado, esta función también lo configurará, respetando PYTHONUSERBASE.

Added in version 3.2.

site.getusersitepackages()

Retorna la ruta del directorio base del usuario USER_SITE. Si este aún no fue inicializado, esta función también lo configurará, respetando USER_BASE. Para determinar si los paquetes específicos del sitio de usuario fueron añadidos a sys.path debe usarse ENABLE_USER_SITE.

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

Si se llama sin argumentos, imprimirá el contenido de sys.path en la salida estándar, seguido del valor de USER_BASE y si el directorio existe, entonces lo mismo para USER_SITE, y finalmente el valor de ENABLE_USER_SITE.

--user-base

Imprime la ruta al directorio base del usuario.

--user-site

Imprime la ruta al directorio site-packages del usuario.

Si se dan ambas opciones, la ruta del directorio base y la del directorio site-packages del usuario se imprimirán (siempre en este orden), separados por os.pathsep.

Si se da alguna opción, el script saldrá con uno de estos valores: 0 si el directorio site-packages del usuario está habilitado, 1 si fue deshabilitado por el usuario, 2 si está deshabilitado por razones de seguridad o por un administrador, y un valor mayor que 2 si hay un error.

Ver también