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Issue #15502: Bring the importlib ABCs into line with the current state of the import protocols given PEP 420. Original patch by Eric Snow.

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This commit is contained in:
Nick Coghlan 2012-08-02 21:26:03 +10:00
parent a90f311d05
commit 8a9080feff
5 changed files with 127 additions and 65 deletions
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71
Doc/library/importlib.rst
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@ -125,26 +125,9 @@ are also provided to help in implementing the core ABCs.
.. class:: Finder
An abstract base class representing a :term:`finder`.
See :pep:`302` for the exact definition for a finder.
.. method:: find_loader(self, fullname):
An abstract 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 sequence may be empty. When present, `find_loader()` is
preferred over `find_module()`.
.. versionadded: 3.3
.. method:: find_module(fullname, path=None)
An abstract method for finding a :term:`loader` for the specified
module. If the :term:`finder` is found on :data:`sys.meta_path` and the
module to be searched for is a subpackage or module then *path* will
be the value of :attr:`__path__` from the parent package. If a loader
cannot be found, ``None`` is returned.
An abstract base class representing a :term:`finder`. Finder
implementations should derive from (or register with) the more specific
:class:`MetaPathFinder` or :class:`PathEntryFinder` ABCs.
.. method:: invalidate_caches()
@ -152,6 +135,40 @@ are also provided to help in implementing the core ABCs.
cache used by the finder. Used by :func:`invalidate_caches()` when
invalidating the caches of all cached finders.
.. versionchanged:: 3.3
The API signatures for meta path finders and path entry finders
were separated by PEP 420. Accordingly, the Finder ABC no
longer requires implementation of a ``find_module()`` method.
.. class:: MetaPathFinder(Finder)
An abstract base class representing a :term:`meta path finder`.
.. versionadded:: 3.3
.. method:: find_module(fullname, path)
An abstract method for finding a :term:`loader` for the specified
module. If this is a top-level import, *path* will be ``None``.
Otheriwse, 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.
.. class:: PathEntryFinder(Finder)
An abstract base class representing a :term:`path entry finder`.
.. versionadded:: 3.3
.. method:: find_loader(self, fullname):
An abstract 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 sequence may be empty.
.. class:: Loader
@ -569,8 +586,8 @@ find and load modules.
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.Finder` and :class:`importlib.abc.InspectLoader`
ABCs.
:class:`importlib.abc.MetaPathFinder` and
:class:`importlib.abc.InspectLoader` ABCs.
Only class methods are defined by this class to alleviate the need for
instantiation.
@ -579,8 +596,8 @@ find and load modules.
.. class:: FrozenImporter
An :term:`importer` for frozen modules. This class implements the
:class:`importlib.abc.Finder` and :class:`importlib.abc.InspectLoader`
ABCs.
:class:`importlib.abc.MetaPathFinder` and
:class:`importlib.abc.InspectLoader` ABCs.
Only class methods are defined by this class to alleviate the need for
instantiation.
@ -589,7 +606,7 @@ find and load modules.
.. class:: PathFinder
:term:`Finder` for :data:`sys.path`. This class implements the
:class:`importlib.abc.Finder` ABC.
:class:`importlib.abc.MetaPathFinder` ABC.
This class does not perfectly mirror the semantics of :keyword:`import` in
terms of :data:`sys.path`. No implicit path hooks are assumed for
@ -616,8 +633,8 @@ find and load modules.
.. class:: FileFinder(path, \*loader_details)
A concrete implementation of :class:`importlib.abc.Finder` which caches
results from the file system.
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.

82
Lib/importlib/abc.py
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@ -23,6 +23,61 @@ def _register(abstract_cls, *classes):
abstract_cls.register(frozen_cls)
class Finder(metaclass=abc.ABCMeta):
"""Common abstract base class for import finders.
Finder implementations should derive from the more specific
MetaPathFinder or PathEntryFinder ABCs rather than directly from Finder.
"""
def find_module(self, fullname, path=None):
"""An optional legacy method that should find a module.
The fullname is a str and the optional path is a str or None.
Returns a Loader object.
The path finder will use this method only if find_loader() does
not exist. It may optionally be implemented for compatibility
with legacy third party reimplementations of the import system.
"""
raise NotImplementedError
# invalidate_caches() is a completely optional method, so no default
# implementation is provided. See the docs for details.
class MetaPathFinder(Finder):
"""Abstract base class for import finders on sys.meta_path."""
@abc.abstractmethod
def find_module(self, fullname, path):
"""Abstract method which when implemented should find a module.
The fullname is a str and the path is a str or None.
Returns a Loader object.
"""
raise NotImplementedError
_register(MetaPathFinder, machinery.BuiltinImporter, machinery.FrozenImporter,
machinery.PathFinder)
class PathEntryFinder(Finder):
"""Abstract base class for path entry finders used by PathFinder."""
@abc.abstractmethod
def find_loader(self, fullname):
"""Abstract method which when implemented returns a module loader.
The fullname is a str. Returns a 2-tuple of (Loader, portion) where
portion is a sequence of file system locations contributing to part of
a namespace package. The sequence may be empty.
"""
raise NotImplementedError
_register(PathEntryFinder, machinery.FileFinder)
class Loader(metaclass=abc.ABCMeta):
"""Abstract base class for import loaders."""
@ -40,33 +95,6 @@ class Loader(metaclass=abc.ABCMeta):
raise NotImplementedError
class Finder(metaclass=abc.ABCMeta):
"""Abstract base class for import finders."""
@abc.abstractmethod
def find_loader(self, fullname):
"""Abstract method which when implemented returns a module loader.
The fullname is a str. Returns a 2-tuple of (Loader, portion) where
portion is a sequence of file system locations contributing to part of
a namespace package. The sequence may be empty. When present,
`find_loader()` is preferred over `find_module()`.
"""
raise NotImplementedError
@abc.abstractmethod
def find_module(self, fullname, path=None):
"""Abstract method which when implemented should find a module.
The fullname is a str and the optional path is a str or None.
Returns a Loader object. This method is only called if
`find_loader()` is not present.
"""
raise NotImplementedError
_register(Finder, machinery.BuiltinImporter, machinery.FrozenImporter,
machinery.PathFinder, machinery.FileFinder)
class ResourceLoader(Loader):
"""Abstract base class for loaders which can return data from their

23
Lib/test/test_importlib/source/test_abc_loader.py
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@ -778,23 +778,32 @@ class SourceLoaderGetSourceTests(unittest.TestCase):
expect = io.IncrementalNewlineDecoder(None, True).decode(source)
self.assertEqual(mock.get_source(name), expect)
class AbstractMethodImplTests(unittest.TestCase):
"""Test the concrete abstractmethod implementations."""
class MetaPathFinder(abc.MetaPathFinder):
def find_module(self, fullname, path):
super().find_module(fullname, path)
class PathEntryFinder(abc.PathEntryFinder):
def find_module(self, _):
super().find_module(_)
def find_loader(self, _):
super().find_loader(_)
class Finder(abc.Finder):
def find_module(self, fullname, path):
super().find_module(fullname, path)
class Loader(abc.Loader):
def load_module(self, fullname):
super().load_module(fullname)
def module_repr(self, module):
super().module_repr(module)
class Finder(abc.Finder):
def find_module(self, _):
super().find_module(_)
def find_loader(self, _):
super().find_loader(_)
class ResourceLoader(Loader, abc.ResourceLoader):
def get_data(self, _):
super().get_data(_)

7
Lib/test/test_importlib/test_abc.py
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@ -30,11 +30,16 @@ class InheritanceTests:
"{0} is not a superclass of {1}".format(superclass, self.__test))
class Finder(InheritanceTests, unittest.TestCase):
class MetaPathFinder(InheritanceTests, unittest.TestCase):
superclasses = [abc.Finder]
subclasses = [machinery.BuiltinImporter, machinery.FrozenImporter,
machinery.PathFinder]
class PathEntryFinder(InheritanceTests, unittest.TestCase):
superclasses = [abc.Finder]
subclasses = [machinery.FileFinder]
class Loader(InheritanceTests, unittest.TestCase):

3
Misc/NEWS
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@ -72,6 +72,9 @@ Core and Builtins
Library
-------
- Issue #15502: Bring the importlib ABCs into line with the current state
of the import protocols given PEP 420. Original patch by Eric Snow.
- Issue #15499: Launching a webbrowser in Unix used to sleep for a few
seconds. Original patch by Anton Barkovsky.