/usr/share/doc/python3-docs/html/_sources/library
Edit: /usr/share/doc/python3-docs/html/_sources/library/importlib.rst.txt (53563B)
:mod:`importlib` --- The implementation of :keyword:`import`
============================================================
.. module:: importlib
:synopsis: The implementation of the import machinery.
.. moduleauthor:: Brett Cannon
.. sectionauthor:: Brett Cannon
.. versionadded:: 3.1
**Source code:** :source:`Lib/importlib/__init__.py`
--------------
Introduction
------------
The purpose of the :mod:`importlib` package is two-fold. One is to provide the
implementation of the :keyword:`import` statement (and thus, by extension, the
:func:`__import__` function) in Python source code. This provides an
implementation of :keyword:`import` which is portable to any Python
interpreter. This also provides an implementation which is easier to
comprehend than one implemented in a programming language other than Python.
Two, the components to implement :keyword:`import` are exposed in this
package, making it easier for users to create their own custom objects (known
generically as an :term:`importer`) to participate in the import process.
.. seealso::
:ref:`import`
The language reference for the :keyword:`import` statement.
`Packages specification `__
Original specification of packages. Some semantics have changed since
the writing of this document (e.g. redirecting based on ``None``
in :data:`sys.modules`).
The :func:`.__import__` function
The :keyword:`import` statement is syntactic sugar for this function.
:pep:`235`
Import on Case-Insensitive Platforms
:pep:`263`
Defining Python Source Code Encodings
:pep:`302`
New Import Hooks
:pep:`328`
Imports: Multi-Line and Absolute/Relative
:pep:`366`
Main module explicit relative imports
:pep:`420`
Implicit namespace packages
:pep:`451`
A ModuleSpec Type for the Import System
:pep:`488`
Elimination of PYO files
:pep:`489`
Multi-phase extension module initialization
:pep:`3120`
Using UTF-8 as the Default Source Encoding
:pep:`3147`
PYC Repository Directories
Functions
---------
.. function:: __import__(name, globals=None, locals=None, fromlist=(), level=0)
An implementation of the built-in :func:`__import__` function.
.. note::
Programmatic importing of modules should use :func:`import_module`
instead of this function.
.. function:: import_module(name, package=None)
Import a module. The *name* argument specifies what module to
import in absolute or relative terms
(e.g. either ``pkg.mod`` or ``..mod``). If the name is
specified in relative terms, then the *package* argument must be set to
the name of the package which is to act as the anchor for resolving the
package name (e.g. ``import_module('..mod', 'pkg.subpkg')`` will import
``pkg.mod``).
The :func:`import_module` function acts as a simplifying wrapper around
:func:`importlib.__import__`. This means all semantics of the function are
derived from :func:`importlib.__import__`. The most important difference
between these two functions is that :func:`import_module` returns the
specified package or module (e.g. ``pkg.mod``), while :func:`__import__`
returns the top-level package or module (e.g. ``pkg``).
If you are dynamically importing a module that was created since the
interpreter began execution (e.g., created a Python source file), you may
need to call :func:`invalidate_caches` in order for the new module to be
noticed by the import system.
.. versionchanged:: 3.3
Parent packages are automatically imported.
.. function:: find_loader(name, path=None)
Find the loader for a module, optionally within the specified *path*. If the
module is in :attr:`sys.modules`, then ``sys.modules[name].__loader__`` is
returned (unless the loader would be ``None`` or is not set, in which case
:exc:`ValueError` is raised). Otherwise a search using :attr:`sys.meta_path`
is done. ``None`` is returned if no loader is found.
A dotted name does not have its parents implicitly imported as that requires
loading them and that may not be desired. To properly import a submodule you
will need to import all parent packages of the submodule and use the correct
argument to *path*.
.. versionadded:: 3.3
.. versionchanged:: 3.4
If ``__loader__`` is not set, raise :exc:`ValueError`, just like when the
attribute is set to ``None``.
.. deprecated:: 3.4
Use :func:`importlib.util.find_spec` instead.
.. function:: invalidate_caches()
Invalidate the internal caches of finders stored at
:data:`sys.meta_path`. If a finder implements ``invalidate_caches()`` then it
will be called to perform the invalidation. This function should be called
if any modules are created/installed while your program is running to
guarantee all finders will notice the new module's existence.
.. versionadded:: 3.3
.. function:: reload(module)
Reload a previously imported *module*. The argument must be a module object,
so it must have been successfully imported before. This is useful if you
have edited the module source file using an external editor and want to try
out the new version without leaving the Python interpreter. The return value
is the module object (which can be different if re-importing causes a
different object to be placed in :data:`sys.modules`).
When :func:`reload` is executed:
* Python module's code is recompiled and the module-level code re-executed,
defining a new set of objects which are bound to names in the module's
dictionary by reusing the :term:`loader` which originally loaded the
module. The ``init`` function of extension modules is not called a second
time.
* As with all other objects in Python the old objects are only reclaimed
after their reference counts drop to zero.
* The names in the module namespace are updated to point to any new or
changed objects.
* Other references to the old objects (such as names external to the module) are
not rebound to refer to the new objects and must be updated in each namespace
where they occur if that is desired.
There are a number of other caveats:
When a module is reloaded, its dictionary (containing the module's global
variables) is retained. Redefinitions of names will override the old
definitions, so this is generally not a problem. If the new version of a
module does not define a name that was defined by the old version, the old
definition remains. This feature can be used to the module's advantage if it
maintains a global table or cache of objects --- with a :keyword:`try`
statement it can test for the table's presence and skip its initialization if
desired::
try:
cache
except NameError:
cache = {}
It is generally not very useful to reload built-in or dynamically loaded
modules. Reloading :mod:`sys`, :mod:`__main__`, :mod:`builtins` and other
key modules is not recommended. In many cases extension modules are not
designed to be initialized more than once, and may fail in arbitrary ways
when reloaded.
If a module imports objects from another module using :keyword:`from` ...
:keyword:`import` ..., calling :func:`reload` for the other module does not
redefine the objects imported from it --- one way around this is to
re-execute the :keyword:`from` statement, another is to use :keyword:`import`
and qualified names (*module.name*) instead.
If a module instantiates instances of a class, reloading the module that
defines the class does not affect the method definitions of the instances ---
they continue to use the old class definition. The same is true for derived
classes.
.. versionadded:: 3.4
:mod:`importlib.abc` -- Abstract base classes related to import
---------------------------------------------------------------
.. module:: importlib.abc
:synopsis: Abstract base classes related to import
**Source code:** :source:`Lib/importlib/abc.py`
--------------
The :mod:`importlib.abc` module contains all of the core abstract base classes
used by :keyword:`import`. Some subclasses of the core abstract base classes
are also provided to help in implementing the core ABCs.
ABC hierarchy::
object
+-- Finder (deprecated)
| +-- MetaPathFinder
| +-- PathEntryFinder
+-- Loader
+-- ResourceLoader --------+
+-- InspectLoader |
+-- ExecutionLoader --+
+-- FileLoader
+-- SourceLoader
.. class:: Finder
An abstract base class representing a :term:`finder`.
.. deprecated:: 3.3
Use :class:`MetaPathFinder` or :class:`PathEntryFinder` instead.
.. abstractmethod:: find_module(fullname, path=None)
An abstract method for finding a :term:`loader` for the specified
module. Originally specified in :pep:`302`, this method was meant
for use in :data:`sys.meta_path` and in the path-based import subsystem.
.. versionchanged:: 3.4
Returns ``None`` when called instead of raising
:exc:`NotImplementedError`.
.. class:: MetaPathFinder
An abstract base class representing a :term:`meta path finder`. For
compatibility, this is a subclass of :class:`Finder`.
.. versionadded:: 3.3
.. method:: find_spec(fullname, path, target=None)
An abstract method for finding a :term:`spec ` for
the specified module. If this is a top-level import, *path* will
be ``None``. Otherwise, this is a search for a subpackage or
module and *path* will be the value of :attr:`__path__` from the
parent package. If a spec cannot be found, ``None`` is returned.
When passed in, ``target`` is a module object that the finder may
use to make a more educated guess about what spec to return.
.. versionadded:: 3.4
.. method:: find_module(fullname, path)
A legacy method for finding a :term:`loader` for the specified
module. If this is a top-level import, *path* will be ``None``.
Otherwise, this is a search for a subpackage or module and *path*
will be the value of :attr:`__path__` from the parent
package. If a loader cannot be found, ``None`` is returned.
If :meth:`find_spec` is defined, backwards-compatible functionality is
provided.
.. versionchanged:: 3.4
Returns ``None`` when called instead of raising
:exc:`NotImplementedError`. Can use :meth:`find_spec` to provide
functionality.
.. deprecated:: 3.4
Use :meth:`find_spec` instead.
.. method:: invalidate_caches()
An optional method which, when called, should invalidate any internal
cache used by the finder. Used by :func:`importlib.invalidate_caches`
when invalidating the caches of all finders on :data:`sys.meta_path`.
.. versionchanged:: 3.4
Returns ``None`` when called instead of ``NotImplemented``.
.. class:: PathEntryFinder
An abstract base class representing a :term:`path entry finder`. Though
it bears some similarities to :class:`MetaPathFinder`, ``PathEntryFinder``
is meant for use only within the path-based import subsystem provided
by :class:`PathFinder`. This ABC is a subclass of :class:`Finder` for
compatibility reasons only.
.. versionadded:: 3.3
.. method:: find_spec(fullname, target=None)
An abstract method for finding a :term:`spec ` for
the specified module. The finder will search for the module only
within the :term:`path entry` to which it is assigned. If a spec
cannot be found, ``None`` is returned. When passed in, ``target``
is a module object that the finder may use to make a more educated
guess about what spec to return.
.. versionadded:: 3.4
.. method:: find_loader(fullname)
A legacy method for finding a :term:`loader` for the specified
module. Returns a 2-tuple of ``(loader, portion)`` where ``portion``
is a sequence of file system locations contributing to part of a namespace
package. The loader may be ``None`` while specifying ``portion`` to
signify the contribution of the file system locations to a namespace
package. An empty list can be used for ``portion`` to signify the loader
is not part of a namespace package. If ``loader`` is ``None`` and
``portion`` is the empty list then no loader or location for a namespace
package were found (i.e. failure to find anything for the module).
If :meth:`find_spec` is defined then backwards-compatible functionality is
provided.
.. versionchanged:: 3.4
Returns ``(None, [])`` instead of raising :exc:`NotImplementedError`.
Uses :meth:`find_spec` when available to provide functionality.
.. deprecated:: 3.4
Use :meth:`find_spec` instead.
.. method:: find_module(fullname)
A concrete implementation of :meth:`Finder.find_module` which is
equivalent to ``self.find_loader(fullname)[0]``.
.. deprecated:: 3.4
Use :meth:`find_spec` instead.
.. method:: invalidate_caches()
An optional method which, when called, should invalidate any internal
cache used by the finder. Used by :meth:`PathFinder.invalidate_caches`
when invalidating the caches of all cached finders.
.. class:: Loader
An abstract base class for a :term:`loader`.
See :pep:`302` for the exact definition for a loader.
.. method:: create_module(spec)
A method that returns the module object to use when
importing a module. This method may return ``None``,
indicating that default module creation semantics should take place.
.. versionadded:: 3.4
.. versionchanged:: 3.5
Starting in Python 3.6, this method will not be optional when
:meth:`exec_module` is defined.
.. method:: exec_module(module)
An abstract method that executes the module in its own namespace
when a module is imported or reloaded. The module should already
be initialized when ``exec_module()`` is called. When this method exists,
:meth:`~importlib.abc.Loader.create_module` must be defined.
.. versionadded:: 3.4
.. versionchanged:: 3.6
:meth:`~importlib.abc.Loader.create_module` must also be defined.
.. method:: load_module(fullname)
A legacy method for loading a module. If the module cannot be
loaded, :exc:`ImportError` is raised, otherwise the loaded module is
returned.
If the requested module already exists in :data:`sys.modules`, that
module should be used and reloaded.
Otherwise the loader should create a new module and insert it into
:data:`sys.modules` before any loading begins, to prevent recursion
from the import. If the loader inserted a module and the load fails, it
must be removed by the loader from :data:`sys.modules`; modules already
in :data:`sys.modules` before the loader began execution should be left
alone (see :func:`importlib.util.module_for_loader`).
The loader should set several attributes on the module.
(Note that some of these attributes can change when a module is
reloaded):
- :attr:`__name__`
The name of the module.
- :attr:`__file__`
The path to where the module data is stored (not set for built-in
modules).
- :attr:`__cached__`
The path to where a compiled version of the module is/should be
stored (not set when the attribute would be inappropriate).
- :attr:`__path__`
A list of strings specifying the search path within a
package. This attribute is not set on modules.
- :attr:`__package__`
The parent package for the module/package. If the module is
top-level then it has a value of the empty string. The
:func:`importlib.util.module_for_loader` decorator can handle the
details for :attr:`__package__`.
- :attr:`__loader__`
The loader used to load the module. The
:func:`importlib.util.module_for_loader` decorator can handle the
details for :attr:`__package__`.
When :meth:`exec_module` is available then backwards-compatible
functionality is provided.
.. versionchanged:: 3.4
Raise :exc:`ImportError` when called instead of
:exc:`NotImplementedError`. Functionality provided when
:meth:`exec_module` is available.
.. deprecated:: 3.4
The recommended API for loading a module is :meth:`exec_module`
(and :meth:`create_module`). Loaders should implement
it instead of load_module(). The import machinery takes care of
all the other responsibilities of load_module() when exec_module()
is implemented.
.. method:: module_repr(module)
A legacy method which when implemented calculates and returns the
given module's repr, as a string. The module type's default repr() will
use the result of this method as appropriate.
.. versionadded:: 3.3
.. versionchanged:: 3.4
Made optional instead of an abstractmethod.
.. deprecated:: 3.4
The import machinery now takes care of this automatically.
.. class:: ResourceLoader
An abstract base class for a :term:`loader` which implements the optional
:pep:`302` protocol for loading arbitrary resources from the storage
back-end.
.. abstractmethod:: get_data(path)
An abstract method to return the bytes for the data located at *path*.
Loaders that have a file-like storage back-end
that allows storing arbitrary data
can implement this abstract method to give direct access
to the data stored. :exc:`OSError` is to be raised if the *path* cannot
be found. The *path* is expected to be constructed using a module's
:attr:`__file__` attribute or an item from a package's :attr:`__path__`.
.. versionchanged:: 3.4
Raises :exc:`OSError` instead of :exc:`NotImplementedError`.
.. class:: InspectLoader
An abstract base class for a :term:`loader` which implements the optional
:pep:`302` protocol for loaders that inspect modules.
.. method:: get_code(fullname)
Return the code object for a module, or ``None`` if the module does not
have a code object (as would be the case, for example, for a built-in
module). Raise an :exc:`ImportError` if loader cannot find the
requested module.
.. note::
While the method has a default implementation, it is suggested that
it be overridden if possible for performance.
.. index::
single: universal newlines; importlib.abc.InspectLoader.get_source method
.. versionchanged:: 3.4
No longer abstract and a concrete implementation is provided.
.. abstractmethod:: get_source(fullname)
An abstract method to return the source of a module. It is returned as
a text string using :term:`universal newlines`, translating all
recognized line separators into ``'\n'`` characters. Returns ``None``
if no source is available (e.g. a built-in module). Raises
:exc:`ImportError` if the loader cannot find the module specified.
.. versionchanged:: 3.4
Raises :exc:`ImportError` instead of :exc:`NotImplementedError`.
.. method:: is_package(fullname)
An abstract method to return a true value if the module is a package, a
false value otherwise. :exc:`ImportError` is raised if the
:term:`loader` cannot find the module.
.. versionchanged:: 3.4
Raises :exc:`ImportError` instead of :exc:`NotImplementedError`.
.. staticmethod:: source_to_code(data, path='')
Create a code object from Python source.
The *data* argument can be whatever the :func:`compile` function
supports (i.e. string or bytes). The *path* argument should be
the "path" to where the source code originated from, which can be an
abstract concept (e.g. location in a zip file).
With the subsequent code object one can execute it in a module by
running ``exec(code, module.__dict__)``.
.. versionadded:: 3.4
.. versionchanged:: 3.5
Made the method static.
.. method:: exec_module(module)
Implementation of :meth:`Loader.exec_module`.
.. versionadded:: 3.4
.. method:: load_module(fullname)
Implementation of :meth:`Loader.load_module`.
.. deprecated:: 3.4
use :meth:`exec_module` instead.
.. class:: ExecutionLoader
An abstract base class which inherits from :class:`InspectLoader` that,
when implemented, helps a module to be executed as a script. The ABC
represents an optional :pep:`302` protocol.
.. abstractmethod:: get_filename(fullname)
An abstract method that is to return the value of :attr:`__file__` for
the specified module. If no path is available, :exc:`ImportError` is
raised.
If source code is available, then the method should return the path to
the source file, regardless of whether a bytecode was used to load the
module.
.. versionchanged:: 3.4
Raises :exc:`ImportError` instead of :exc:`NotImplementedError`.
.. class:: FileLoader(fullname, path)
An abstract base class which inherits from :class:`ResourceLoader` and
:class:`ExecutionLoader`, providing concrete implementations of
:meth:`ResourceLoader.get_data` and :meth:`ExecutionLoader.get_filename`.
The *fullname* argument is a fully resolved name of the module the loader is
to handle. The *path* argument is the path to the file for the module.
.. versionadded:: 3.3
.. attribute:: name
The name of the module the loader can handle.
.. attribute:: path
Path to the file of the module.
.. method:: load_module(fullname)
Calls super's ``load_module()``.
.. deprecated:: 3.4
Use :meth:`Loader.exec_module` instead.
.. abstractmethod:: get_filename(fullname)
Returns :attr:`path`.
.. abstractmethod:: get_data(path)
Reads *path* as a binary file and returns the bytes from it.
.. class:: SourceLoader
An abstract base class for implementing source (and optionally bytecode)
file loading. The class inherits from both :class:`ResourceLoader` and
:class:`ExecutionLoader`, requiring the implementation of:
* :meth:`ResourceLoader.get_data`
* :meth:`ExecutionLoader.get_filename`
Should only return the path to the source file; sourceless
loading is not supported.
The abstract methods defined by this class are to add optional bytecode
file support. Not implementing these optional methods (or causing them to
raise :exc:`NotImplementedError`) causes the loader to
only work with source code. Implementing the methods allows the loader to
work with source *and* bytecode files; it does not allow for *sourceless*
loading where only bytecode is provided. Bytecode files are an
optimization to speed up loading by removing the parsing step of Python's
compiler, and so no bytecode-specific API is exposed.
.. method:: path_stats(path)
Optional abstract method which returns a :class:`dict` containing
metadata about the specified path. Supported dictionary keys are:
- ``'mtime'`` (mandatory): an integer or floating-point number
representing the modification time of the source code;
- ``'size'`` (optional): the size in bytes of the source code.
Any other keys in the dictionary are ignored, to allow for future
extensions. If the path cannot be handled, :exc:`OSError` is raised.
.. versionadded:: 3.3
.. versionchanged:: 3.4
Raise :exc:`OSError` instead of :exc:`NotImplementedError`.
.. method:: path_mtime(path)
Optional abstract method which returns the modification time for the
specified path.
.. deprecated:: 3.3
This method is deprecated in favour of :meth:`path_stats`. You don't
have to implement it, but it is still available for compatibility
purposes. Raise :exc:`OSError` if the path cannot be handled.
.. versionchanged:: 3.4
Raise :exc:`OSError` instead of :exc:`NotImplementedError`.
.. method:: set_data(path, data)
Optional abstract method which writes the specified bytes to a file
path. Any intermediate directories which do not exist are to be created
automatically.
When writing to the path fails because the path is read-only
(:attr:`errno.EACCES`/:exc:`PermissionError`), do not propagate the
exception.
.. versionchanged:: 3.4
No longer raises :exc:`NotImplementedError` when called.
.. method:: get_code(fullname)
Concrete implementation of :meth:`InspectLoader.get_code`.
.. method:: exec_module(module)
Concrete implementation of :meth:`Loader.exec_module`.
.. versionadded:: 3.4
.. method:: load_module(fullname)
Concrete implementation of :meth:`Loader.load_module`.
.. deprecated:: 3.4
Use :meth:`exec_module` instead.
.. method:: get_source(fullname)
Concrete implementation of :meth:`InspectLoader.get_source`.
.. method:: is_package(fullname)
Concrete implementation of :meth:`InspectLoader.is_package`. A module
is determined to be a package if its file path (as provided by
:meth:`ExecutionLoader.get_filename`) is a file named
``__init__`` when the file extension is removed **and** the module name
itself does not end in ``__init__``.
:mod:`importlib.machinery` -- Importers and path hooks
------------------------------------------------------
.. module:: importlib.machinery
:synopsis: Importers and path hooks
**Source code:** :source:`Lib/importlib/machinery.py`
--------------
This module contains the various objects that help :keyword:`import`
find and load modules.
.. attribute:: SOURCE_SUFFIXES
A list of strings representing the recognized file suffixes for source
modules.
.. versionadded:: 3.3
.. attribute:: DEBUG_BYTECODE_SUFFIXES
A list of strings representing the file suffixes for non-optimized bytecode
modules.
.. versionadded:: 3.3
.. deprecated:: 3.5
Use :attr:`BYTECODE_SUFFIXES` instead.
.. attribute:: OPTIMIZED_BYTECODE_SUFFIXES
A list of strings representing the file suffixes for optimized bytecode
modules.
.. versionadded:: 3.3
.. deprecated:: 3.5
Use :attr:`BYTECODE_SUFFIXES` instead.
.. attribute:: BYTECODE_SUFFIXES
A list of strings representing the recognized file suffixes for bytecode
modules (including the leading dot).
.. versionadded:: 3.3
.. versionchanged:: 3.5
The value is no longer dependent on ``__debug__``.
.. attribute:: EXTENSION_SUFFIXES
A list of strings representing the recognized file suffixes for
extension modules.
.. versionadded:: 3.3
.. function:: all_suffixes()
Returns a combined list of strings representing all file suffixes for
modules recognized by the standard import machinery. This is a
helper for code which simply needs to know if a filesystem path
potentially refers to a module without needing any details on the kind
of module (for example, :func:`inspect.getmodulename`).
.. versionadded:: 3.3
.. class:: BuiltinImporter
An :term:`importer` for built-in modules. All known built-in modules are
listed in :data:`sys.builtin_module_names`. This class implements the
:class:`importlib.abc.MetaPathFinder` and
:class:`importlib.abc.InspectLoader` ABCs.
Only class methods are defined by this class to alleviate the need for
instantiation.
.. versionchanged:: 3.5
As part of :pep:`489`, the builtin importer now implements
:meth:`Loader.create_module` and :meth:`Loader.exec_module`
.. class:: FrozenImporter
An :term:`importer` for frozen modules. This class implements the
:class:`importlib.abc.MetaPathFinder` and
:class:`importlib.abc.InspectLoader` ABCs.
Only class methods are defined by this class to alleviate the need for
instantiation.
.. class:: WindowsRegistryFinder
:term:`Finder` for modules declared in the Windows registry. This class
implements the :class:`importlib.abc.MetaPathFinder` ABC.
Only class methods are defined by this class to alleviate the need for
instantiation.
.. versionadded:: 3.3
.. deprecated:: 3.6
Use :mod:`site` configuration instead. Future versions of Python may
not enable this finder by default.
.. class:: PathFinder
A :term:`Finder` for :data:`sys.path` and package ``__path__`` attributes.
This class implements the :class:`importlib.abc.MetaPathFinder` ABC.
Only class methods are defined by this class to alleviate the need for
instantiation.
.. classmethod:: find_spec(fullname, path=None, target=None)
Class method that attempts to find a :term:`spec `
for the module specified by *fullname* on :data:`sys.path` or, if
defined, on *path*. For each path entry that is searched,
:data:`sys.path_importer_cache` is checked. If a non-false object
is found then it is used as the :term:`path entry finder` to look
for the module being searched for. If no entry is found in
:data:`sys.path_importer_cache`, then :data:`sys.path_hooks` is
searched for a finder for the path entry and, if found, is stored
in :data:`sys.path_importer_cache` along with being queried about
the module. If no finder is ever found then ``None`` is both
stored in the cache and returned.
.. versionadded:: 3.4
.. versionchanged:: 3.5
If the current working directory -- represented by an empty string --
is no longer valid then ``None`` is returned but no value is cached
in :data:`sys.path_importer_cache`.
.. classmethod:: find_module(fullname, path=None)
A legacy wrapper around :meth:`find_spec`.
.. deprecated:: 3.4
Use :meth:`find_spec` instead.
.. classmethod:: invalidate_caches()
Calls :meth:`importlib.abc.PathEntryFinder.invalidate_caches` on all
finders stored in :attr:`sys.path_importer_cache`.
.. versionchanged:: 3.4
Calls objects in :data:`sys.path_hooks` with the current working
directory for ``''`` (i.e. the empty string).
.. class:: FileFinder(path, \*loader_details)
A concrete implementation of :class:`importlib.abc.PathEntryFinder` which
caches results from the file system.
The *path* argument is the directory for which the finder is in charge of
searching.
The *loader_details* argument is a variable number of 2-item tuples each
containing a loader and a sequence of file suffixes the loader recognizes.
The loaders are expected to be callables which accept two arguments of
the module's name and the path to the file found.
The finder will cache the directory contents as necessary, making stat calls
for each module search to verify the cache is not outdated. Because cache
staleness relies upon the granularity of the operating system's state
information of the file system, there is a potential race condition of
searching for a module, creating a new file, and then searching for the
module the new file represents. If the operations happen fast enough to fit
within the granularity of stat calls, then the module search will fail. To
prevent this from happening, when you create a module dynamically, make sure
to call :func:`importlib.invalidate_caches`.
.. versionadded:: 3.3
.. attribute:: path
The path the finder will search in.
.. method:: find_spec(fullname, target=None)
Attempt to find the spec to handle *fullname* within :attr:`path`.
.. versionadded:: 3.4
.. method:: find_loader(fullname)
Attempt to find the loader to handle *fullname* within :attr:`path`.
.. method:: invalidate_caches()
Clear out the internal cache.
.. classmethod:: path_hook(\*loader_details)
A class method which returns a closure for use on :attr:`sys.path_hooks`.
An instance of :class:`FileFinder` is returned by the closure using the
path argument given to the closure directly and *loader_details*
indirectly.
If the argument to the closure is not an existing directory,
:exc:`ImportError` is raised.
.. class:: SourceFileLoader(fullname, path)
A concrete implementation of :class:`importlib.abc.SourceLoader` by
subclassing :class:`importlib.abc.FileLoader` and providing some concrete
implementations of other methods.
.. versionadded:: 3.3
.. attribute:: name
The name of the module that this loader will handle.
.. attribute:: path
The path to the source file.
.. method:: is_package(fullname)
Return true if :attr:`path` appears to be for a package.
.. method:: path_stats(path)
Concrete implementation of :meth:`importlib.abc.SourceLoader.path_stats`.
.. method:: set_data(path, data)
Concrete implementation of :meth:`importlib.abc.SourceLoader.set_data`.
.. method:: load_module(name=None)
Concrete implementation of :meth:`importlib.abc.Loader.load_module` where
specifying the name of the module to load is optional.
.. deprecated:: 3.6
Use :meth:`importlib.abc.Loader.exec_module` instead.
.. class:: SourcelessFileLoader(fullname, path)
A concrete implementation of :class:`importlib.abc.FileLoader` which can
import bytecode files (i.e. no source code files exist).
Please note that direct use of bytecode files (and thus not source code
files) inhibits your modules from being usable by all Python
implementations or new versions of Python which change the bytecode
format.
.. versionadded:: 3.3
.. attribute:: name
The name of the module the loader will handle.
.. attribute:: path
The path to the bytecode file.
.. method:: is_package(fullname)
Determines if the module is a package based on :attr:`path`.
.. method:: get_code(fullname)
Returns the code object for :attr:`name` created from :attr:`path`.
.. method:: get_source(fullname)
Returns ``None`` as bytecode files have no source when this loader is
used.
.. method:: load_module(name=None)
Concrete implementation of :meth:`importlib.abc.Loader.load_module` where
specifying the name of the module to load is optional.
.. deprecated:: 3.6
Use :meth:`importlib.abc.Loader.exec_module` instead.
.. class:: ExtensionFileLoader(fullname, path)
A concrete implementation of :class:`importlib.abc.ExecutionLoader` for
extension modules.
The *fullname* argument specifies the name of the module the loader is to
support. The *path* argument is the path to the extension module's file.
.. versionadded:: 3.3
.. attribute:: name
Name of the module the loader supports.
.. attribute:: path
Path to the extension module.
.. method:: create_module(spec)
Creates the module object from the given specification in accordance
with :pep:`489`.
.. versionadded:: 3.5
.. method:: exec_module(module)
Initializes the given module object in accordance with :pep:`489`.
.. versionadded:: 3.5
.. method:: is_package(fullname)
Returns ``True`` if the file path points to a package's ``__init__``
module based on :attr:`EXTENSION_SUFFIXES`.
.. method:: get_code(fullname)
Returns ``None`` as extension modules lack a code object.
.. method:: get_source(fullname)
Returns ``None`` as extension modules do not have source code.
.. method:: get_filename(fullname)
Returns :attr:`path`.
.. versionadded:: 3.4
.. class:: ModuleSpec(name, loader, *, origin=None, loader_state=None, is_package=None)
A specification for a module's import-system-related state. This is
typically exposed as the module's ``__spec__`` attribute. In the
descriptions below, the names in parentheses give the corresponding
attribute available directly on the module object.
E.g. ``module.__spec__.origin == module.__file__``. Note however that
while the *values* are usually equivalent, they can differ since there is
no synchronization between the two objects. Thus it is possible to update
the module's ``__path__`` at runtime, and this will not be automatically
reflected in ``__spec__.submodule_search_locations``.
.. versionadded:: 3.4
.. attribute:: name
(``__name__``)
A string for the fully-qualified name of the module.
.. attribute:: loader
(``__loader__``)
The loader to use for loading. For namespace packages this should be
set to ``None``.
.. attribute:: origin
(``__file__``)
Name of the place from which the module is loaded, e.g. "builtin" for
built-in modules and the filename for modules loaded from source.
Normally "origin" should be set, but it may be ``None`` (the default)
which indicates it is unspecified.
.. attribute:: submodule_search_locations
(``__path__``)
List of strings for where to find submodules, if a package (``None``
otherwise).
.. attribute:: loader_state
Container of extra module-specific data for use during loading (or
``None``).
.. attribute:: cached
(``__cached__``)
String for where the compiled module should be stored (or ``None``).
.. attribute:: parent
(``__package__``)
(Read-only) Fully-qualified name of the package to which the module
belongs as a submodule (or ``None``).
.. attribute:: has_location
Boolean indicating whether or not the module's "origin"
attribute refers to a loadable location.
:mod:`importlib.util` -- Utility code for importers
---------------------------------------------------
.. module:: importlib.util
:synopsis: Utility code for importers
**Source code:** :source:`Lib/importlib/util.py`
--------------
This module contains the various objects that help in the construction of
an :term:`importer`.
.. attribute:: MAGIC_NUMBER
The bytes which represent the bytecode version number. If you need help with
loading/writing bytecode then consider :class:`importlib.abc.SourceLoader`.
.. versionadded:: 3.4
.. function:: cache_from_source(path, debug_override=None, *, optimization=None)
Return the :pep:`3147`/:pep:`488` path to the byte-compiled file associated
with the source *path*. For example, if *path* is ``/foo/bar/baz.py`` the return
value would be ``/foo/bar/__pycache__/baz.cpython-32.pyc`` for Python 3.2.
The ``cpython-32`` string comes from the current magic tag (see
:func:`get_tag`; if :attr:`sys.implementation.cache_tag` is not defined then
:exc:`NotImplementedError` will be raised).
The *optimization* parameter is used to specify the optimization level of the
bytecode file. An empty string represents no optimization, so
``/foo/bar/baz.py`` with an *optimization* of ``''`` will result in a
bytecode path of ``/foo/bar/__pycache__/baz.cpython-32.pyc``. ``None`` causes
the interpter's optimization level to be used. Any other value's string
representation being used, so ``/foo/bar/baz.py`` with an *optimization* of
``2`` will lead to the bytecode path of
``/foo/bar/__pycache__/baz.cpython-32.opt-2.pyc``. The string representation
of *optimization* can only be alphanumeric, else :exc:`ValueError` is raised.
The *debug_override* parameter is deprecated and can be used to override
the system's value for ``__debug__``. A ``True`` value is the equivalent of
setting *optimization* to the empty string. A ``False`` value is the same as
setting *optimization* to ``1``. If both *debug_override* an *optimization*
are not ``None`` then :exc:`TypeError` is raised.
.. versionadded:: 3.4
.. versionchanged:: 3.5
The *optimization* parameter was added and the *debug_override* parameter
was deprecated.
.. versionchanged:: 3.6
Accepts a :term:`path-like object`.
.. function:: source_from_cache(path)
Given the *path* to a :pep:`3147` file name, return the associated source code
file path. For example, if *path* is
``/foo/bar/__pycache__/baz.cpython-32.pyc`` the returned path would be
``/foo/bar/baz.py``. *path* need not exist, however if it does not conform
to :pep:`3147` or :pep:`488` format, a ``ValueError`` is raised. If
:attr:`sys.implementation.cache_tag` is not defined,
:exc:`NotImplementedError` is raised.
.. versionadded:: 3.4
.. versionchanged:: 3.6
Accepts a :term:`path-like object`.
.. function:: decode_source(source_bytes)
Decode the given bytes representing source code and return it as a string
with universal newlines (as required by
:meth:`importlib.abc.InspectLoader.get_source`).
.. versionadded:: 3.4
.. function:: resolve_name(name, package)
Resolve a relative module name to an absolute one.
If **name** has no leading dots, then **name** is simply returned. This
allows for usage such as
``importlib.util.resolve_name('sys', __package__)`` without doing a
check to see if the **package** argument is needed.
:exc:`ValueError` is raised if **name** is a relative module name but
package is a false value (e.g. ``None`` or the empty string).
:exc:`ValueError` is also raised a relative name would escape its containing
package (e.g. requesting ``..bacon`` from within the ``spam`` package).
.. versionadded:: 3.3
.. function:: find_spec(name, package=None)
Find the :term:`spec ` for a module, optionally relative to
the specified **package** name. If the module is in :attr:`sys.modules`,
then ``sys.modules[name].__spec__`` is returned (unless the spec would be
``None`` or is not set, in which case :exc:`ValueError` is raised).
Otherwise a search using :attr:`sys.meta_path` is done. ``None`` is
returned if no spec is found.
If **name** is for a submodule (contains a dot), the parent module is
automatically imported.
**name** and **package** work the same as for :func:`import_module`.
.. versionadded:: 3.4
.. function:: module_from_spec(spec)
Create a new module based on **spec** and
:meth:`spec.loader.create_module `.
If :meth:`spec.loader.create_module `
does not return ``None``, then any pre-existing attributes will not be reset.
Also, no :exc:`AttributeError` will be raised if triggered while accessing
**spec** or setting an attribute on the module.
This function is preferred over using :class:`types.ModuleType` to create a
new module as **spec** is used to set as many import-controlled attributes on
the module as possible.
.. versionadded:: 3.5
.. decorator:: module_for_loader
A :term:`decorator` for :meth:`importlib.abc.Loader.load_module`
to handle selecting the proper
module object to load with. The decorated method is expected to have a call
signature taking two positional arguments
(e.g. ``load_module(self, module)``) for which the second argument
will be the module **object** to be used by the loader.
Note that the decorator will not work on static methods because of the
assumption of two arguments.
The decorated method will take in the **name** of the module to be loaded
as expected for a :term:`loader`. If the module is not found in
:data:`sys.modules` then a new one is constructed. Regardless of where the
module came from, :attr:`__loader__` set to **self** and :attr:`__package__`
is set based on what :meth:`importlib.abc.InspectLoader.is_package` returns
(if available). These attributes are set unconditionally to support
reloading.
If an exception is raised by the decorated method and a module was added to
:data:`sys.modules`, then the module will be removed to prevent a partially
initialized module from being in left in :data:`sys.modules`. If the module
was already in :data:`sys.modules` then it is left alone.
.. versionchanged:: 3.3
:attr:`__loader__` and :attr:`__package__` are automatically set
(when possible).
.. versionchanged:: 3.4
Set :attr:`__name__`, :attr:`__loader__` :attr:`__package__`
unconditionally to support reloading.
.. deprecated:: 3.4
The import machinery now directly performs all the functionality
provided by this function.
.. decorator:: set_loader
A :term:`decorator` for :meth:`importlib.abc.Loader.load_module`
to set the :attr:`__loader__`
attribute on the returned module. If the attribute is already set the
decorator does nothing. It is assumed that the first positional argument to
the wrapped method (i.e. ``self``) is what :attr:`__loader__` should be set
to.
.. versionchanged:: 3.4
Set ``__loader__`` if set to ``None``, as if the attribute does not
exist.
.. deprecated:: 3.4
The import machinery takes care of this automatically.
.. decorator:: set_package
A :term:`decorator` for :meth:`importlib.abc.Loader.load_module` to set the
:attr:`__package__` attribute on the returned module. If :attr:`__package__`
is set and has a value other than ``None`` it will not be changed.
.. deprecated:: 3.4
The import machinery takes care of this automatically.
.. function:: spec_from_loader(name, loader, *, origin=None, is_package=None)
A factory function for creating a :class:`ModuleSpec` instance based
on a loader. The parameters have the same meaning as they do for
ModuleSpec. The function uses available :term:`loader` APIs, such as
:meth:`InspectLoader.is_package`, to fill in any missing
information on the spec.
.. versionadded:: 3.4
.. function:: spec_from_file_location(name, location, *, loader=None, submodule_search_locations=None)
A factory function for creating a :class:`ModuleSpec` instance based
on the path to a file. Missing information will be filled in on the
spec by making use of loader APIs and by the implication that the
module will be file-based.
.. versionadded:: 3.4
.. versionchanged:: 3.6
Accepts a :term:`path-like object`.
.. class:: LazyLoader(loader)
A class which postpones the execution of the loader of a module until the
module has an attribute accessed.
This class **only** works with loaders that define
:meth:`~importlib.abc.Loader.exec_module` as control over what module type
is used for the module is required. For those same reasons, the loader's
:meth:`~importlib.abc.Loader.create_module` method must return ``None`` or a
type for which its ``__class__`` attribute can be mutated along with not
using :term:`slots <__slots__>`. Finally, modules which substitute the object
placed into :attr:`sys.modules` will not work as there is no way to properly
replace the module references throughout the interpreter safely;
:exc:`ValueError` is raised if such a substitution is detected.
.. note::
For projects where startup time is critical, this class allows for
potentially minimizing the cost of loading a module if it is never used.
For projects where startup time is not essential then use of this class is
**heavily** discouraged due to error messages created during loading being
postponed and thus occurring out of context.
.. versionadded:: 3.5
.. versionchanged:: 3.6
Began calling :meth:`~importlib.abc.Loader.create_module`, removing the
compatibility warning for :class:`importlib.machinery.BuiltinImporter` and
:class:`importlib.machinery.ExtensionFileLoader`.
.. classmethod:: factory(loader)
A static method which returns a callable that creates a lazy loader. This
is meant to be used in situations where the loader is passed by class
instead of by instance.
::
suffixes = importlib.machinery.SOURCE_SUFFIXES
loader = importlib.machinery.SourceFileLoader
lazy_loader = importlib.util.LazyLoader.factory(loader)
finder = importlib.machinery.FileFinder(path, (lazy_loader, suffixes))
.. _importlib-examples:
Examples
--------
Importing programmatically
''''''''''''''''''''''''''
To programmatically import a module, use :func:`importlib.import_module`.
::
import importlib
itertools = importlib.import_module('itertools')
Checking if a module can be imported
''''''''''''''''''''''''''''''''''''
If you need to find out if a module can be imported without actually doing the
import, then you should use :func:`importlib.util.find_spec`.
::
import importlib.util
import sys
# For illustrative purposes.
name = 'itertools'
spec = importlib.util.find_spec(name)
if spec is None:
print("can't find the itertools module")
else:
# If you chose to perform the actual import ...
module = importlib.util.module_from_spec(spec)
spec.loader.exec_module(module)
# Adding the module to sys.modules is optional.
sys.modules[name] = module
Importing a source file directly
''''''''''''''''''''''''''''''''
To import a Python source file directly, use the following recipe
(Python 3.4 and newer only)::
import importlib.util
import sys
# For illustrative purposes.
import tokenize
file_path = tokenize.__file__
module_name = tokenize.__name__
spec = importlib.util.spec_from_file_location(module_name, file_path)
module = importlib.util.module_from_spec(spec)
spec.loader.exec_module(module)
# Optional; only necessary if you want to be able to import the module
# by name later.
sys.modules[module_name] = module
Setting up an importer
''''''''''''''''''''''
For deep customizations of import, you typically want to implement an
:term:`importer`. This means managing both the :term:`finder` and :term:`loader`
side of things. For finders there are two flavours to choose from depending on
your needs: a :term:`meta path finder` or a :term:`path entry finder`. The
former is what you would put on :attr:`sys.meta_path` while the latter is what
you create using a :term:`path entry hook` on :attr:`sys.path_hooks` which works
with :attr:`sys.path` entries to potentially create a finder. This example will
show you how to register your own importers so that import will use them (for
creating an importer for yourself, read the documentation for the appropriate
classes defined within this package)::
import importlib.machinery
import sys
# For illustrative purposes only.
SpamMetaPathFinder = importlib.machinery.PathFinder
SpamPathEntryFinder = importlib.machinery.FileFinder
loader_details = (importlib.machinery.SourceFileLoader,
importlib.machinery.SOURCE_SUFFIXES)
# Setting up a meta path finder.
# Make sure to put the finder in the proper location in the list in terms of
# priority.
sys.meta_path.append(SpamMetaPathFinder)
# Setting up a path entry finder.
# Make sure to put the path hook in the proper location in the list in terms
# of priority.
sys.path_hooks.append(SpamPathEntryFinder.path_hook(loader_details))
Approximating :func:`importlib.import_module`
'''''''''''''''''''''''''''''''''''''''''''''
Import itself is implemented in Python code, making it possible to
expose most of the import machinery through importlib. The following
helps illustrate the various APIs that importlib exposes by providing an
approximate implementation of
:func:`importlib.import_module` (Python 3.4 and newer for the importlib usage,
Python 3.6 and newer for other parts of the code).
::
import importlib.util
import sys
def import_module(name, package=None):
"""An approximate implementation of import."""
absolute_name = importlib.util.resolve_name(name, package)
try:
return sys.modules[absolute_name]
except KeyError:
pass
path = None
if '.' in absolute_name:
parent_name, _, child_name = absolute_name.rpartition('.')
parent_module = import_module(parent_name)
path = parent_module.spec.submodule_search_locations
for finder in sys.meta_path:
spec = finder.find_spec(absolute_name, path)
if spec is not None:
break
else:
raise ImportError(f'No module named {absolute_name!r}')
module = importlib.util.module_from_spec(spec)
spec.loader.exec_module(module)
sys.modules[absolute_name] = module
if path is not None:
setattr(parent_module, child_name, module)
return module