: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`
The purpose of the :mod:`importlib` package is three-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.
Three, the package contains modules exposing additional functionality for managing aspects of Python packages:
- :mod:`importlib.metadata` presents access to metadata from third-party distributions.
- :mod:`importlib.resources` provides routines for accessing non-code "resources" from Python packages.
.. 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.
:ref:`sys-path-init`
The initialization of :data:`sys.path`.
: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
.. 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:: 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
.. versionchanged:: 3.10
Namespace packages created/installed in a different :data:`sys.path`
location after the same namespace was already imported are noticed.
.. 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:`~importlib.machinery.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
+-- MetaPathFinder
+-- PathEntryFinder
+-- Loader
+-- ResourceLoader --------+
+-- InspectLoader |
+-- ExecutionLoader --+
+-- FileLoader
+-- SourceLoader
An abstract base class representing a :term:`meta path finder`.
.. versionadded:: 3.3
.. versionchanged:: 3.10 No longer a subclass of :class:`!Finder`.
.. 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. :func:`importlib.util.spec_from_loader` may be useful for implementing concrete ``MetaPathFinders``. .. versionadded:: 3.4
.. 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 :data:`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:`importlib.machinery.PathFinder`.
.. versionadded:: 3.3
.. versionchanged:: 3.10 No longer a subclass of :class:`!Finder`.
.. 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. :func:`importlib.util.spec_from_loader` may be useful for implementing concrete ``PathEntryFinders``. .. versionadded:: 3.4
.. method:: invalidate_caches() An optional method which, when called, should invalidate any internal cache used by the finder. Used by :meth:`importlib.machinery.PathFinder.invalidate_caches` when invalidating the caches of all cached finders.
An abstract base class for a :term:`loader`. See PEP 302 for the exact definition for a loader.
Loaders that wish to support resource reading should implement a :meth:`get_resource_reader` method as specified by :class:`importlib.resources.abc.ResourceReader`.
.. versionchanged:: 3.7 Introduced the optional :meth:`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:: 3.6
This method is no longer 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 :meth:`exec_module` is called. When this method exists,
:meth:`create_module` must be defined.
.. versionadded:: 3.4
.. versionchanged:: 3.6
:meth:`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.
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 module's fully qualified name.
It is ``'__main__'`` for an executed module.
- :attr:`__file__`
The location the :term:`loader` used to load the module.
For example, for modules loaded from a .py file this is the filename.
It is not set on all modules (e.g. built-in modules).
- :attr:`__cached__`
The filename of a compiled version of the module's code.
It is not set on all modules (e.g. built-in modules).
- :attr:`__path__`
The list of locations where the package's submodules will be found.
Most of the time this is a single directory.
The import system passes this attribute to ``__import__()`` and to finders
in the same way as :data:`sys.path` but just for the package.
It is not set on non-package modules so it can be used
as an indicator that the module is a package.
- :attr:`__package__`
The fully qualified name of the package the module is in (or the
empty string for a top-level module).
If the module is a package then this is the same as :attr:`__name__`.
- :attr:`__loader__`
The :term:`loader` used to load the module.
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
:meth:`load_module`. The import machinery takes care of all the
other responsibilities of :meth:`load_module` when
:meth:`exec_module` is implemented.
An abstract base class for a :term:`loader` which implements the optional PEP 302 protocol for loading arbitrary resources from the storage back-end.
.. deprecated:: 3.7 This ABC is deprecated in favour of supporting resource loading through :class:`importlib.resources.abc.ResourceReader`.
.. 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`.
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 optional 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='<string>')
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.
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`.
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.
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
(:const:`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__``.
Superseded by TraversableResources
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_reader(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
.. deprecated-removed:: 3.12 3.14 Use :class:`importlib.resources.abc.TraversableResources` instead.
.. 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 object with a subset of :class:`pathlib.Path` methods suitable for traversing directories and opening files.
For a representation of the object on the file-system, use :meth:`importlib.resources.as_file`.
.. versionadded:: 3.9
.. deprecated-removed:: 3.12 3.14 Use :class:`importlib.resources.abc.Traversable` instead.
.. attribute:: name Abstract. The base name of this object without any parent references.
.. abstractmethod:: iterdir() Yield ``Traversable`` objects in ``self``.
.. abstractmethod:: is_dir() Return ``True`` if ``self`` is a directory.
.. abstractmethod:: is_file() Return ``True`` if ``self`` is a file.
.. abstractmethod:: joinpath(child) Return Traversable child in ``self``.
.. abstractmethod:: __truediv__(child) Return ``Traversable`` child in ``self``.
.. abstractmethod:: open(mode='r', *args, **kwargs) *mode* may be 'r' or 'rb' to open as text or binary. Return a handle suitable for reading (same as :attr:`pathlib.Path.open`). When opening as text, accepts encoding parameters such as those accepted by :attr:`io.TextIOWrapper`.
.. method:: read_bytes() Read contents of ``self`` as bytes.
.. method:: read_text(encoding=None) Read contents of ``self`` as text.
An abstract base class for resource readers capable of serving the :meth:`importlib.resources.files` interface. Subclasses :class:`importlib.resources.abc.ResourceReader` and provides concrete implementations of the :class:`importlib.resources.abc.ResourceReader`'s abstract methods. Therefore, any loader supplying :class:`importlib.abc.TraversableResources` also supplies ResourceReader.
Loaders that wish to support resource reading are expected to implement this interface.
.. versionadded:: 3.9
.. deprecated-removed:: 3.12 3.14 Use :class:`importlib.resources.abc.TraversableResources` instead.
.. abstractmethod:: files() Returns a :class:`importlib.resources.abc.Traversable` object for the loaded package.
: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.
.. versionchanged:: 3.4 Gained :meth:`~Loader.create_module` and :meth:`~Loader.exec_module` methods.
:term:`Finder <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 <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:: 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:: invalidate_caches() Clear out the internal cache.
.. classmethod:: path_hook(*loader_details) A class method which returns a closure for use on :data:`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.
Note that, by default, importing an extension module will fail in subinterpreters if it doesn't implement multi-phase init (see PEP 489), even if it would otherwise import successfully.
.. versionadded:: 3.3
.. versionchanged:: 3.12 Multi-phase init is now required for use in subinterpreters.
.. 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
A concrete implementation of :class:`importlib.abc.InspectLoader` for
namespace packages. This is an alias for a private class and is only made
public for introspecting the __loader__ attribute on namespace
packages:
>>> from importlib.machinery import NamespaceLoader >>> import my_namespace >>> isinstance(my_namespace.__loader__, NamespaceLoader) True >>> import importlib.abc >>> isinstance(my_namespace.__loader__, importlib.abc.Loader) True
.. versionadded:: 3.11
A specialization of :class:`importlib.machinery.ExtensionFileLoader` that is able to load extension modules in Framework format.
For compatibility with the iOS App Store, all binary modules in an iOS app
must be dynamic libraries, contained in a framework with appropriate
metadata, stored in the Frameworks folder of the packaged app. There can
be only a single binary per framework, and there can be no executable binary
material outside the Frameworks folder.
To accomodate this requirement, when running on iOS, extension module
binaries are not packaged as .so files on sys.path, but as
individual standalone frameworks. To discover those frameworks, this loader
is be registered against the .fwork file extension, with a .fwork
file acting as a placeholder in the original location of the binary on
sys.path. The .fwork file contains the path of the actual binary in
the Frameworks folder, relative to the app bundle. To allow for
resolving a framework-packaged binary back to the original location, the
framework is expected to contain a .origin file that contains the
location of the .fwork file, relative to the app bundle.
For example, consider the case of an import from foo.bar import _whiz,
where _whiz is implemented with the binary module
sources/foo/bar/_whiz.abi3.so, with sources being the location
registered on sys.path, relative to the application bundle. This module
must be distributed as
Frameworks/foo.bar._whiz.framework/foo.bar._whiz (creating the framework
name from the full import path of the module), with an Info.plist file
in the .framework directory identifying the binary as a framework. The
foo.bar._whiz module would be represented in the original location with
a sources/foo/bar/_whiz.abi3.fwork marker file, containing the path
Frameworks/foo.bar._whiz/foo.bar._whiz. The framework would also contain
Frameworks/foo.bar._whiz.framework/foo.bar._whiz.origin, containing the
path to the .fwork file.
When a module is loaded with this loader, the __file__ for the module
will report as the location of the .fwork file. This allows code to use
the __file__ of a module as an anchor for file system traveral.
However, the spec origin will reference the location of the actual binary
in the .framework folder.
The Xcode project building the app is responsible for converting any .so
files from wherever they exist in the PYTHONPATH into frameworks in the
Frameworks folder (including stripping extensions from the module file,
the addition of framework metadata, and signing the resulting framework),
and creating the .fwork and .origin files. This will usually be done
with a build step in the Xcode project; see the iOS documentation for
details on how to construct this build step.
.. versionadded:: 3.13
.. availability:: iOS.
.. attribute:: name Name of the module the loader supports.
.. attribute:: path Path to the ``.fwork`` file for the extension module.
: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 interpreter's optimization level to be used. Any other value's string
representation is 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', __spec__.parent)`` without doing a
check to see if the **package** argument is needed.
:exc:`ImportError` is raised if **name** is a relative module name but
**package** is a false value (e.g. ``None`` or the empty string).
:exc:`ImportError` is also raised if a relative name would escape its
containing package (e.g. requesting ``..bacon`` from within the ``spam``
package).
.. versionadded:: 3.3
.. versionchanged:: 3.9
To improve consistency with import statements, raise
:exc:`ImportError` instead of :exc:`ValueError` for invalid relative
import attempts.
.. 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 :data:`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 :data:`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
.. function:: spec_from_loader(name, loader, *, origin=None, is_package=None) A factory function for creating a :class:`~importlib.machinery.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:`~importlib.machinery.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
.. function:: _incompatible_extension_module_restrictions(*, disable_check)
A context manager that can temporarily skip the compatibility check
for extension modules. By default the check is enabled and will fail
when a single-phase init module is imported in a subinterpreter.
It will also fail for a multi-phase init module that doesn't
explicitly support a per-interpreter GIL, when imported
in an interpreter with its own GIL.
Note that this function is meant to accommodate an unusual case;
one which is likely to eventually go away. There's is a pretty good
chance this is not what you were looking for.
You can get the same effect as this function by implementing the
basic interface of multi-phase init (:pep:`489`) and lying about
support for multiple interpreters (or per-interpreter GIL).
.. warning::
Using this function to disable the check can lead to
unexpected behavior and even crashes. It should only be used during
extension module development.
.. versionadded:: 3.12
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 :data:`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 class 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))
To programmatically import a module, use :func:`importlib.import_module`.
import importlib
itertools = importlib.import_module('itertools')
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`.
Note that if name is a submodule (contains a dot),
:func:`importlib.util.find_spec` will import the parent module.
import importlib.util
import sys
# For illustrative purposes.
name = 'itertools'
if name in sys.modules:
print(f"{name!r} already in sys.modules")
elif (spec := importlib.util.find_spec(name)) is not None:
# If you chose to perform the actual import ...
module = importlib.util.module_from_spec(spec)
sys.modules[name] = module
spec.loader.exec_module(module)
print(f"{name!r} has been imported")
else:
print(f"can't find the {name!r} module")
To import a Python source file directly, use the following recipe:
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) sys.modules[module_name] = module spec.loader.exec_module(module)
The example below shows how to implement lazy imports:
>>> import importlib.util
>>> import sys
>>> def lazy_import(name):
... spec = importlib.util.find_spec(name)
... loader = importlib.util.LazyLoader(spec.loader)
... spec.loader = loader
... module = importlib.util.module_from_spec(spec)
... sys.modules[name] = module
... loader.exec_module(module)
... return module
...
>>> lazy_typing = lazy_import("typing")
>>> #lazy_typing is a real module object,
>>> #but it is not loaded in memory yet.
>>> lazy_typing.TYPE_CHECKING
False
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 :data:`sys.meta_path` while the latter is what you create using a :term:`path entry hook` on :data:`sys.path_hooks` which works with :data:`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`:
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)
sys.modules[absolute_name] = module
spec.loader.exec_module(module)
if path is not None:
setattr(parent_module, child_name, module)
return module