Introduce importlib.abc. The module contains various ABCs related to imports
(mostly stuff specified by PEP 302). There are two ABCs, PyLoader and
PyPycLoader, which help with implementing source and source/bytecode loaders by
implementing load_module in terms of other methods. This removes a lot of
gritty details loaders typically have to worry about.
diff --git a/Doc/library/importlib.rst b/Doc/library/importlib.rst
index 1481302..eb9fd00 100644
--- a/Doc/library/importlib.rst
+++ b/Doc/library/importlib.rst
@@ -82,6 +82,175 @@
occuring from to already be imported (i.e., *package* must already be
imported).
+:mod:`importlib.abc` -- Abstract base classes related to import
+---------------------------------------------------------------
+
+.. module:: importlib.abc
+ :synopsis: Abstract base classes related to import
+
+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.
+
+
+.. class:: Finder
+
+ An abstract base class representing a :term:`finder`.
+
+ ..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* is set
+ to the value of :attr:`__path__` from the parent package. If a loader
+ cannot be found, :keyword:`None` is returned.
+
+ The exact definition of a :term:`finder` can be found in :pep:`302`.
+
+
+.. class:: Loader
+
+ An abstract base class for a :term:`loader`.
+
+ ..method:: load_module(fullname)
+
+ An abstract 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 is already exists in :data:`sys.modules`, that
+ module should be used and reloaded.
+ Otherwise a new module is to be created by the loader and inserted into
+ :data:`sys.modules`before any loading begins to prevent recursion from
+ the import. If the loader inserted into 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 :func:`importlib.util.module_for_loader` decorator handles
+ all of these details.
+
+ The loader is expected to set several attributes on the module when
+ adding a new module to :data:`sys.modules`.
+
+ - :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:`__path__`
+ Set to 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.set_package` decorator can handle the details
+ for :attr:`__package__`.
+
+ - :attr:`__loader__`
+ Set to the loader used to load the module.
+
+ See :pep:`302` for the exact definition for a loader.
+
+
+.. class:: ResourceLoader
+
+ An abstract base class for a :term:`loader` which implements the optional
+ :pep:`302` protocol for loading arbitrary resources from the storage
+ back-end.
+
+ ..method:: 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 can implement this
+ abstract method to give direct access
+ to the data stored. :exc:`IOError` is to be raised if the *path* cannot
+ be found. The *path* is expected to be constructed using a module's
+ :attr:`__path__` attribute or an item from :attr:`__path__`.
+
+
+.. class:: InspectLoader
+
+ An abstract base class for a :term:`loader` which implements the optional
+ :pep:`302` protocol for loaders which inspect modules.
+
+ ..method:: is_package(fullname)
+
+ An abstract method to return a true value if the module is a package, a
+ false value otherwise. :exc:`ImportError` is raised if the
+ :term:`loader` cannot find the module.
+
+ ..method:: get_source(fullname)
+
+ An abstract method to return the source of a module. It is returned as
+ a string with universal newline support. Returns :keyword:`None` if no
+ source is available (e.g. a built-in module). Raises :exc:`ImportError`
+ if the loader cannot find the module specified.
+
+ ..method:: get_code(fullname)
+
+ An abstract method to return the :class:`code` object for a module.
+ :keyword:`None` is returned if the module does not have a code object
+ (e.g. built-in module). :exc:`ImportError` is raised if loader cannot
+ find the requested module.
+
+
+.. class:: PyLoader
+
+ An abstract base class inheriting from :class:`importlib.abc.InspectLoader`
+ and :class:`importlib.abc.ResourceLoader` designed to ease the loading of
+ Python source modules (bytecode is not handled; see
+ :class:`importlib.abc.PyPycLoader` for a source/bytecode ABC). A subclass
+ implementing this ABC will only need to worry about exposing how the source
+ code is stored; all other details for loading Python source code will be
+ handled by the concrete implementations of key methods.
+
+ ..method:: source_path(fullname)
+
+ An abstract method that returns the path to the source code for a
+ module. Should return :keyword:`None` if there is no source code.
+ :exc:`ImportError` if the module cannot be found.
+
+ ..method:: load_module(fullname)
+
+ A concrete implementation of :meth:`importlib.abc.Loader.load_module`
+ that loads Python source code.
+
+ ..method:: get_code(fullname)
+
+ A concrete implementation of
+ :meth:`importlib.abc.InspectLoader.get_code` that creates code objects
+ from Python source code.
+
+
+.. class:: PyPycLoader
+
+ An abstract base class inheriting from :class:`importlib.abc.PyLoader`.
+ This ABC is meant to help in creating loaders that support both Python
+ source and bytecode.
+
+ ..method:: source_mtime(fullname)
+
+ An abstract method which returns the modification time for the source
+ code of the specified module. The modification time should be an
+ integer. If there is no source code, return :keyword:`None. If the
+ module cannot be found then :exc:`ImportError` is raised.
+
+ ..method:: bytecode_path(fullname)
+
+ An abstract method which returns the path to the bytecode for the
+ specified module. :keyword:`None` is returned if there is no bytecode.
+ :exc:`ImportError` is raised if the module is not found.
+
+ ..method:: write_bytecode(fullname, bytecode)
+
+ An abstract method which has the loader write *bytecode* for future
+ use. If the bytecode is written, return :keyword:`True`. Return
+ :keyword:`False` if the bytecode could not be written. This method
+ should not be called if :data:`sys.dont_write_bytecode` is true.
+
+
:mod:`importlib.machinery` -- Importers and path hooks
------------------------------------------------------
@@ -93,44 +262,27 @@
.. class:: BuiltinImporter
- :term:`Importer` for built-in modules. All known built-in modules are
- listed in :data:`sys.builtin_module_names`.
+ 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.Loader` ABCs.
Only class methods are defined by this class to alleviate the need for
instantiation.
- .. classmethod:: find_module(fullname, path=None)
-
- Class method that allows this class to be a :term:`finder` for built-in
- modules.
-
- .. classmethod:: load_module(fullname)
-
- Class method that allows this class to be a :term:`loader` for built-in
- modules.
-
.. class:: FrozenImporter
- :term:`Importer` for frozen modules.
+ An :term:`importer` for frozen modules. This class implements the
+ :class:`importlib.abc.Finder` and :class:`importlib.abc.Loader` ABCs.
Only class methods are defined by this class to alleviate the need for
instantiation.
- .. classmethod:: find_module(fullname, path=None)
-
- Class method that allows this class to be a :term:`finder` for frozen
- modules.
-
- .. classmethod:: load_module(fullname)
-
- Class method that allows this class to be a :term:`loader` for frozen
- modules.
-
.. class:: PathFinder
- :term:`Finder` for :data:`sys.path`.
+ :term:`Finder` for :data:`sys.path`. This class implements the
+ :class:`importlib.abc.Finder` 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
@@ -142,15 +294,15 @@
.. classmethod:: find_module(fullname, path=None)
Class method that attempts to find a :term:`loader` for the module
- specified by *fullname* either on :data:`sys.path` or, if defined, on
+ 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 an non-false object is
- found then it is used as the :term:`finder` to query for the module
- being searched for. For no entry is found in
+ found then it is used as the :term:`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.
+ module. If no finder is ever found then :keyword:`None` is returned.
:mod:`importlib.util` -- Utility code for importers
@@ -166,10 +318,11 @@
A :term:`decorator` for a :term:`loader` which handles selecting the proper
module object to load with. The decorated method is expected to have a call
- signature of ``method(self, module_object)`` for which the second argument
- will be the module object to be used by the loader (note that the decorator
+ 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).
+ 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