add property methods to extension for more entry point values

The underlying EntryPoint class has some similar methods to fetch
these values, but they depend on the version of importlib.metadata
that is installed, so this provides a consistent API

Change-Id: I7a1b9541f0e4042a224e49c890ba3c63e8a5a259
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

releasenotes/notes/expose-entry-point-properties-6f2d868d4342fc0d.yaml

@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    Add `extras` and `attr` properties to the `Extension` class to
+    make it easier for consumers to access the underlying properties,
+    regardless of the version of `importlib.metadata` being used.

stevedore/extension.py

@@ -58,6 +58,27 @@ class Extension(object):
         match = self.entry_point.pattern.match(self.entry_point.value)
         return match.group('module')
 
+    @property
+    def extras(self):
+        """The 'extras' settings for the plugin."""
+        # NOTE: The underlying package returns re.Match objects for
+        # some reason. Translate those to the matched strings, which
+        # seem more useful.
+        return [
+            # Python 3.6 returns _sre.SRE_Match objects. Later
+            # versions of python return re.Match objects. Both types
+            # have a 'string' attribute containing the text that
+            # matched the pattern.
+            getattr(e, 'string', e)
+            for e in self.entry_point.extras
+        ]
+
+    @property
+    def attr(self):
+        """The attribute of the module to be loaded."""
+        match = self.entry_point.pattern.match(self.entry_point.value)
+        return match.group('attr')
+
     @property
     def entry_point_target(self):
         """The module and attribute referenced by this extension's entry_point.

stevedore/tests/test_extension.py

@@ -16,6 +16,13 @@
 import operator
 from unittest import mock
 
+try:
+    # For python 3.8 and later
+    import importlib.metadata as importlib_metadata
+except ImportError:
+    # For everyone else
+    import importlib_metadata
+
 from stevedore import exception
 from stevedore import extension
 from stevedore.tests import utils
@@ -241,3 +248,42 @@ class TestLoadRequirementsOldSetuptools(utils.TestCase):
         self.em._load_one_plugin(self.mock_ep, False, (), {},
                                  verify_requirements=False)
         self.mock_ep.load.assert_called_once_with()
+
+
+class TestExtensionProperties(utils.TestCase):
+
+    def setUp(self):
+        self.ext1 = extension.Extension(
+            'name',
+            importlib_metadata.EntryPoint(
+                'name', 'module.name:attribute.name [extra]', 'group_name',
+            ),
+            mock.Mock(),
+            None,
+        )
+        self.ext2 = extension.Extension(
+            'name',
+            importlib_metadata.EntryPoint(
+                'name', 'module:attribute', 'group_name',
+            ),
+            mock.Mock(),
+            None,
+        )
+
+    def test_module_name(self):
+        self.assertEqual('module.name', self.ext1.module_name)
+        self.assertEqual('module', self.ext2.module_name)
+
+    def test_extras(self):
+        self.assertEqual(['[extra]'], self.ext1.extras)
+        self.assertEqual([], self.ext2.extras)
+
+    def test_attr(self):
+        self.assertEqual('attribute.name', self.ext1.attr)
+        self.assertEqual('attribute', self.ext2.attr)
+
+    def test_entry_point_target(self):
+        self.assertEqual('module.name:attribute.name [extra]',
+                         self.ext1.entry_point_target)
+        self.assertEqual('module:attribute',
+                         self.ext2.entry_point_target)