Merge branch 'feature/124-nicer-not-found'

Author: jaraco

importlib_metadata/__init__.py

@@ -55,6 +55,15 @@
 class PackageNotFoundError(ModuleNotFoundError):
     """The package was not found."""
 
+    def __str__(self):
+        tmpl = "No package metadata was found for {self.name}"
+        return tmpl.format(**locals())
+
+    @property
+    def name(self):
+        name, = self.args
+        return name
+
 
 class EntryPoint(
         PyPy_repr,

importlib_metadata/docs/changelog.rst

@@ -2,6 +2,14 @@
  importlib_metadata NEWS
 =========================
 
+v1.7.0
+======
+
+* ``PathNotFoundError`` now has a custom ``__str__``
+  mentioning "package metadata" being missing to help
+  guide users to the cause when the package is installed
+  but no metadata is present. Closes #124.
+
 v1.6.1
 ======
 

importlib_metadata/tests/test_main.py

@@ -35,6 +35,18 @@ def test_for_name_does_not_exist(self):
         with self.assertRaises(PackageNotFoundError):
             Distribution.from_name('does-not-exist')
 
+    def test_package_not_found_mentions_metadata(self):
+        """
+        When a package is not found, that could indicate that the
+        packgae is not installed or that it is installed without
+        metadata. Ensure the exception mentions metadata to help
+        guide users toward the cause. See #124.
+        """
+        with self.assertRaises(PackageNotFoundError) as ctx:
+            Distribution.from_name('does-not-exist')
+
+        assert "metadata" in str(ctx.exception)
+
     def test_new_style_classes(self):
         self.assertIsInstance(Distribution, type)
         self.assertIsInstance(MetadataPathFinder, type)