Implement __getitem__ inference for classes (using the metaclass)

Essentially implement the getitem method in ClassDef which returns the correct value.

Fixes #348

3 files changed, 43 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 1baa403c..558b3857 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -7,6 +7,8 @@ Change log for the astroid package (used to be astng)
       Classes can support keyword arguments, which are passed when
       a class is constructed using ``__new__``.
 
+    * ClassDef now supports __getitem__ inference through the metaclass.
+
     * getitem() method accepts nodes now, instead of Python objects.
 
     * Add support for explicit namespace packages, created with pkg_resources.
diff --git a/astroid/tests/unittest_inference.py b/astroid/tests/unittest_inference.py
index 497b286c..0d1ea266 100644
--- a/astroid/tests/unittest_inference.py
+++ b/astroid/tests/unittest_inference.py
@@ -2537,6 +2537,22 @@ class InferenceTest(resources.SysPathSetup, unittest.TestCase):
         for node in ast_nodes:
             self.assertEqual(next(node.infer()), util.Uninferable)
 
+    def test_metaclass__getitem__(self):
+        ast_node = extract_node('''
+        class Meta(type):
+            def __getitem__(cls, arg):
+                return 24
+        import six
+        @six.add_metaclass(Meta)
+        class A(object):
+            pass
+
+        A['Awesome'] #@
+        ''')
+        inferred = next(ast_node.infer())
+        self.assertIsInstance(inferred, nodes.Const)
+        self.assertEqual(inferred.value, 24)
+
     def test_bin_op_classes(self):
         ast_node = extract_node('''
         class Meta(type):
diff --git a/astroid/tree/scoped_nodes.py b/astroid/tree/scoped_nodes.py
index 257b13d9..31dfc9cd 100644
--- a/astroid/tree/scoped_nodes.py
+++ b/astroid/tree/scoped_nodes.py
@@ -34,6 +34,7 @@ from astroid.interpreter import objects
 from astroid.interpreter import objectmodel
 from astroid.interpreter import runtimeabc
 from astroid.interpreter.util import infer_stmts
+from astroid.interpreter import dunder_lookup
 from astroid import manager
 from astroid.tree import base as treebase
 from astroid.tree import node_classes
@@ -1671,6 +1672,30 @@ class ClassDef(QualifiedNameMixin, base.FilterStmtsMixin,
                 pass
         return False
 
+    def getitem(self, index, context=None):
+        """Return the inference of a subscript.
+
+        This is basically looking up the method in the metaclass and calling it.
+        """
+        try:
+            methods = dunder_lookup.lookup(self, '__getitem__')
+        except (exceptions.AttributeInferenceError,
+                exceptions.NotSupportedError) as error:
+            util.reraise(exceptions.InferenceError(**vars(error)))
+
+        method = methods[0]
+
+        # Create a new callcontext for providing index as an argument.
+        if context:
+            new_context = context.clone()
+        else:
+            new_context = contextmod.InferenceContext()
+
+        new_context.callcontext = contextmod.CallContext(args=[index])
+        new_context.boundnode = self
+
+        return next(method.infer_call_result(self, new_context))
+
     def methods(self):
         """return an iterator on all methods defined in the class and
         its ancestors