AspectList: Add get() method

Usable for bears API

Closes coala#4384

coalib/bearlib/aspects/collections.py

@@ -30,3 +30,19 @@ def __contains__(self, aspect):
             if issubaspect(aspect, item):
                 return True
         return False
+
+    def get(self, aspect):
+        """
+        Return first item that match or contain an aspect. See
+        :meth:`coalib.bearlib.aspects.aspectbase.get` for further example.
+
+        :param aspect: An aspectclass OR name of an aspect.
+        :return:       An aspectclass OR aspectclass instance, depend on
+                       AspectList content. Return None if no match found.
+        """
+        if not isaspect(aspect):
+            aspect = coalib.bearlib.aspects[aspect]
+        try:
+            return next(filter(None, (item.get(aspect) for item in self)))
+        except StopIteration:
+            return None

tests/bearlib/aspects/CollectionsTest.py

@@ -43,3 +43,14 @@ def test__contains__(self):
         assert not isaspect(str)
         exc.match("<class 'str'> is not an "
                   'aspectclass or an instance of an aspectclass')
+
+    def test_get(self):
+        list_of_aspect = AspectList(
+            [Metadata.CommitMessage.Shortlog, Metadata.CommitMessage.Body])
+        self.assertIs(list_of_aspect.get(Metadata.CommitMessage.Shortlog),
+                      Metadata.CommitMessage.Shortlog)
+        self.assertIs(list_of_aspect.get(Metadata.CommitMessage.Body.Length),
+                      Metadata.CommitMessage.Body.Length)
+        self.assertIs(list_of_aspect.get('Body.Length'),
+                      Metadata.CommitMessage.Body.Length)
+        self.assertIsNone(list_of_aspect.get(Metadata))