:mod:`!importlib` --- The implementation of :keyword:`!import`

.. module:: importlib
 :synopsis: The implementation of the import machinery.

.. moduleauthor:: Brett Cannon <brett@python.org>

.. sectionauthor:: Brett Cannon <brett@python.org>

.. 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 <https://www.python.org/doc/essays/packages/>`__
 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:`552`
 Deterministic pycs

 :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
 .. versionchanged:: 3.7
 :exc:`ModuleNotFoundError` is raised when the module being reloaded lacks
 a :class:`ModuleSpec`.

: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

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`.

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 <module 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``.

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 <module 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.

An abstract base class for a :term:`loader`. See :class:`importlib.abc.ResourceReader`.

.. versionchanged:: 3.7
 Introduced the optional ``get_resource_reader()`` method.

.. 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.

An :term:`abstract base class` to provide the ability to read resources.

From the perspective of this ABC, a resource is a binary artifact that is shipped within a package. Typically this is something like a data file that lives next to the __init__.py file of the package. The purpose of this class is to help abstract out the accessing of such data files so that it does not matter if the package and its data file(s) are stored in a e.g. zip file versus on the file system.

For any of methods of this class, a resource argument is expected to be a :term:`path-like object` which represents conceptually just a file name. This means that no subdirectory paths should be included in the resource argument. This is because the location of the package the reader is for, acts as the "directory". Hence the metaphor for directories and file names is packages and resources, respectively. This is also why instances of this class are expected to directly correlate to a specific package (instead of potentially representing multiple packages or a module).

Loaders that wish to support resource reading are expected to provide a method called get_resource_loader(fullname) which returns an object implementing this ABC's interface. If the module specified by fullname is not a package, this method should return :const:`None`. An object compatible with this ABC should only be returned when the specified module is a package.

.. versionadded:: 3.7

.. abstractmethod:: open_resource(resource)

 Returns an opened, :term:`file-like object` for binary reading
 of the *resource*.

 If the resource cannot be found, :exc:`FileNotFoundError` is
 raised.

.. abstractmethod:: resource_path(resource)

 Returns the file system path to the *resource*.

 If the resource does not concretely exist on the file system,
 raise :exc:`FileNotFoundError`.

.. abstractmethod:: is_resource(name)

 Returns ``True`` if the named *name* is considered a resource.
 :exc:`FileNotFoundError` is raised if *name* does not exist.

.. abstractmethod:: contents()

 Returns an :term:`iterable` of strings over the contents of
 the package. Do note that it is not required that all names
 returned by the iterator be actual resources, e.g. it is
 acceptable to return names for which :meth:`is_resource` would
 be false.

 Allowing non-resource names to be returned is to allow for
 situations where how a package and its resources are stored
 are known a priori and the non-resource names would be useful.
 For instance, returning subdirectory names is allowed so that
 when it is known that the package and resources are stored on
 the file system then those subdirectory names can be used
 directly.

 The abstract method returns an iterable of no items.

An abstract base class for a :term:`loader` which implements the optional :term:`loader` which implements the optional

.. 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.

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 :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.

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.resources` -- Resources

.. module:: importlib.resources
 :synopsis: Package resource reading, opening, and access

Source code: :source:`Lib/importlib/resources.py`

.. versionadded:: 3.7

This module leverages Python's import system to provide access to resources within packages. If you can import a package, you can access resources within that package. Resources can be opened or read, in either binary or text mode.

Resources are roughly akin to files inside directories, though it's important to keep in mind that this is just a metaphor. Resources and packages do not have to exist as physical files and directories on the file system.

Loaders that wish to support resource reading should implement a get_resource_reader(fullname) method as specified by :class:`importlib.abc.ResourceReader`.

The following types are defined.

.. data:: Package

 The ``Package`` type is defined as ``Union[str, ModuleType]``. This means
 that where the function describes accepting a ``Package``, you can pass in
 either a string or a module. Module objects must have a resolvable
 ``__spec__.submodule_search_locations`` that is not ``None``.

.. data:: Resource

 This type describes the resource names passed into the various functions
 in this package. This is defined as ``Union[str, os.PathLike]``.

The following functions are available.

.. function:: open_binary(package, resource)

 Open for binary reading the *resource* within *package*.

 *package* is either a name or a module object which conforms to the
 ``Package`` requirements. *resource* is the name of the resource to open
 within *package*; it may not contain path separators and it may not have
 sub-resources (i.e. it cannot be a directory). This function returns a
 ``typing.BinaryIO`` instance, a binary I/O stream open for reading.

.. function:: open_text(package, resource, encoding='utf-8', errors='strict')

 Open for text reading the *resource* within *package*. By default, the
 resource is opened for reading as UTF-8.

 *package* is either a name or a module object which conforms to the
 ``Package`` requirements. *resource* is the name of the resource to open
 within *package*; it may not contain path separators and it may not have
 sub-resources (i.e. it cannot be a directory). *encoding* and *errors*
 have the same meaning as with built-in :func:`open`.

 This function returns a ``typing.TextIO`` instance, a text I/O stream open
 for reading.

.. function:: read_binary(package, resource)

 Read and return the contents of the *resource* within *package* as
 ``bytes``.

 *package* is either a name or a module object which conforms to the
 ``Package`` requirements. *resource* is the name of the resource to open
 within *package*; it may not contain path separators and it may not have
 sub-resources (i.e. it cannot be a directory). This function returns the
 contents of the resource as :class:`bytes`.

.. function:: read_text(package, resource, encoding='utf-8', errors='strict')

 Read and return the contents of *resource* within *package* as a ``str``.
 By default, the contents are read as strict UTF-8.

 *package* is either a name or a module object which conforms to the
 ``Package`` requirements. *resource* is the name of the resource to open
 within *package*; it may not contain path separators and it may not have
 sub-resources (i.e. it cannot be a directory). *encoding* and *errors*
 have the same meaning as with built-in :func:`open`. This function
 returns the contents of the resource as :class:`str`.

.. function:: path(package, resource)

 Return the path to the *resource* as an actual file system path. This
 function returns a context manager for use in a :keyword:`with` statement.
 The context manager provides a :class:`pathlib.Path` object.

 Exiting the context manager cleans up any temporary file created when the
 resource needs to be extracted from e.g. a zip file.

 *package* is either a name or a module object which conforms to the
 ``Package`` requirements. *resource* is the name of the resource to open
 within *package*; it may not contain path separators and it may not have
 sub-resources (i.e. it cannot be a directory).

.. function:: is_resource(package, name)

 Return ``True`` if there is a resource named *name* in the package,
 otherwise ``False``. Remember that directories are *not* resources!
 *package* is either a name or a module object which conforms to the
 ``Package`` requirements.

.. function:: contents(package)

 Return an iterable over the named items within the package. The iterable
 returns :class:`str` resources (e.g. files) and non-resources
 (e.g. directories). The iterable does not recurse into subdirectories.

 *package* is either a name or a module object which conforms to the
 ``Package`` requirements.

: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

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`

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.

: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.

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 <module 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 :data:`sys.path_importer_cache` that define the method.
 Otherwise entries in :data:`sys.path_importer_cache` set to ``None`` are
 deleted.

 .. versionchanged:: 3.7
 Entries of ``None`` in :data:`sys.path_importer_cache` are deleted.

.. versionchanged:: 3.4
 Calls objects in :data:`sys.path_hooks` with the current working
 directory for ``''`` (i.e. the empty string).

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.

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.

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.

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

: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 :exc:`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 <module 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

 .. versionchanged:: 3.7
 Raises :exc:`ModuleNotFoundError` instead of :exc:`AttributeError` if
 **package** is in fact not a package (i.e. lacks a :attr:`__path__`
 attribute).

.. function:: module_from_spec(spec)

 Create a new module based on **spec** and
 :meth:`spec.loader.create_module <importlib.abc.Loader.create_module>`.

 If :meth:`spec.loader.create_module <importlib.abc.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`.

.. function:: source_hash(source_bytes)

 Return the hash of *source_bytes* as bytes. A hash-based ``.pyc`` file embeds
 the :func:`source_hash` of the corresponding source file's contents in its
 header.

 .. versionadded:: 3.7

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.

.. 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))

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 3.5 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:
 msg = f'No module named {absolute_name!r}'
 raise ModuleNotFoundError(msg, name=absolute_name)
 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

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