ShimImporter: implement modern interface

IPython/utils/shimmodule.py

@@ -1,94 +1,81 b''
 """A shim module for deprecated imports
 """
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
+import importlib.abc
+import importlib.util
 import sys
 import types
 from importlib import import_module
 
 from .importstring import import_item
 
 
 class ShimWarning(Warning):
     """A warning to show when a module has moved, and a shim is in its place."""
 
-class ShimImporter(object):
+
+class ShimImporter(importlib.abc.MetaPathFinder):
     """Import hook for a shim.
-    
+
     This ensures that submodule imports return the real target module,
     not a clone that will confuse `is` and `isinstance` checks.
     """
     def __init__(self, src, mirror):
         self.src = src
         self.mirror = mirror
-    
+
     def _mirror_name(self, fullname):
         """get the name of the mirrored module"""
-        
-        return self.mirror + fullname[len(self.src):]
 
-    def find_module(self, fullname, path=None):
-        """Return self if we should be used to import the module."""
-        if fullname.startswith(self.src + '.'):
-            mirror_name = self._mirror_name(fullname)
-            try:
-                mod = import_item(mirror_name)
-            except ImportError:
-                return
-            else:
-                if not isinstance(mod, types.ModuleType):
-                    # not a module
-                    return None
-                return self
+        return self.mirror + fullname[len(self.src) :]
 
-    def load_module(self, fullname):
-        """Import the mirrored module, and insert it into sys.modules"""
-        mirror_name = self._mirror_name(fullname)
-        mod = import_item(mirror_name)
-        sys.modules[fullname] = mod
-        return mod
+    def find_spec(self, fullname, path, target=None):
+        if fullname.startswith(self.src + "."):
+            mirror_name = self._mirror_name(fullname)
+            return importlib.util.find_spec(mirror_name)
 
 
 class ShimModule(types.ModuleType):
 
     def __init__(self, *args, **kwargs):
         self._mirror = kwargs.pop("mirror")
         src = kwargs.pop("src", None)
         if src:
             kwargs['name'] = src.rsplit('.', 1)[-1]
         super(ShimModule, self).__init__(*args, **kwargs)
         # add import hook for descendent modules
         if src:
             sys.meta_path.append(
                 ShimImporter(src=src, mirror=self._mirror)
             )
     
     @property
     def __path__(self):
         return []
     
     @property
     def __spec__(self):
         """Don't produce __spec__ until requested"""
         return import_module(self._mirror).__spec__
     
     def __dir__(self):
         return dir(import_module(self._mirror))
     
     @property
     def __all__(self):
         """Ensure __all__ is always defined"""
         mod = import_module(self._mirror)
         try:
             return mod.__all__
         except AttributeError:
             return [name for name in dir(mod) if not name.startswith('_')]
 
     def __getattr__(self, key):
         # Use the equivalent of import_item(name), see below
         name = "%s.%s" % (self._mirror, key)
         try:
             return import_item(name)
         except ImportError as e:
             raise AttributeError(key) from e

IPython/utils/tests/test_shimmodule.py

@@ -1,10 +1,14 b''
 import pytest
 import sys
 
 from IPython.utils.shimmodule import ShimWarning
 
 
 def test_shim_warning():
     sys.modules.pop('IPython.config', None)
     with pytest.warns(ShimWarning):
         import IPython.config
+
+    import traitlets.config
+
+    assert IPython.config.Config is traitlets.config.Config