Merge branch 'bugfix/86-compatibility' into 'master'

Add compatibility for early Python 3.8 beta releases

Closes #86

See merge request python-devs/importlib_metadata!94

Author: jaraco

importlib_metadata/__init__.py

@@ -178,7 +178,8 @@ def from_name(cls, name):
             metadata cannot be found.
         """
         for resolver in cls._discover_resolvers():
-            dists = resolver(DistributionFinder.Context(name=name))
+            context = DistributionFinder.Context(name=name)
+            dists = cls._maybe_bind(resolver, context)
             dist = next(dists, None)
             if dist is not None:
                 return dist
@@ -200,10 +201,24 @@ def discover(cls, **kwargs):
             raise ValueError("cannot accept context and kwargs")
         context = context or DistributionFinder.Context(**kwargs)
         return itertools.chain.from_iterable(
-            resolver(context)
+            cls._maybe_bind(resolver, context)
             for resolver in cls._discover_resolvers()
             )
 
+    @staticmethod
+    def _maybe_bind(resolver, context):
+        """
+        Only bind the context to the resolver if as a callable,
+        the resolver accepts the context parameter.
+
+        Workaround for
+        https://gitlab.com/python-devs/importlib_metadata/issues/86
+        """
+        try:  # pragma: nocover
+            return resolver(context)
+        except TypeError:  # pragma: nocover
+            return resolver(name=context.name, path=context.path)
+
     @staticmethod
     def at(path):
         """Return a Distribution for the indicated metadata path

importlib_metadata/docs/changelog.rst

@@ -2,6 +2,14 @@
  importlib_metadata NEWS
 =========================
 
+0.23
+====
+* Added a compatibility shim to prevent failures on beta releases
+  of Python before the signature changed to accept the
+  "context" parameter on find_distributions. This workaround
+  will have a limited lifespan, not to extend beyond release of
+  Python 3.8 final.
+
 0.22
 ====
 * Renamed ``package`` parameter to ``distribution_name``