1 files changed, 49 insertions, 21 deletions

diff --git a/Lib/importlib/abc.py b/Lib/importlib/abc.py
index 7fcf2de..5e71758 100644
--- a/Lib/importlib/abc.py
+++ b/Lib/importlib/abc.py
@@ -23,48 +23,76 @@ def _register(abstract_cls, *classes):
             abstract_cls.register(frozen_cls)
 
 
-class Loader(metaclass=abc.ABCMeta):
+class Finder(metaclass=abc.ABCMeta):
 
-    """Abstract base class for import loaders."""
+    """Common abstract base class for import finders.
 
-    @abc.abstractmethod
-    def load_module(self, fullname):
-        """Abstract method which when implemented should load a module.
-        The fullname is a str."""
+    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 module_repr(self, module):
-        """Abstract method which when implemented calculates and returns the
-        given module's repr."""
+    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 Finder(metaclass=abc.ABCMeta):
 
-    """Abstract base class for import finders."""
+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.  When present,
-        `find_loader()` is preferred over `find_module()`.
+        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."""
+
     @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.
-        """
+    def load_module(self, fullname):
+        """Abstract method which when implemented should load a module.
+        The fullname is a str."""
         raise NotImplementedError
 
-_register(Finder, machinery.BuiltinImporter, machinery.FrozenImporter,
-          machinery.PathFinder, machinery.FileFinder)
+    @abc.abstractmethod
+    def module_repr(self, module):
+        """Abstract method which when implemented calculates and returns the
+        given module's repr."""
+        raise NotImplementedError
 
 
 class ResourceLoader(Loader):