Allow finding specific list items by index.

This matches the behavior of JS implementations of mustache. Tested
against mustache.js and Hogan.

>>> context = {"data": ['one', 'two', 'three']}
>>> pystache.render("{{ data.0 }}", context)
'one'

pystache/context.py

@@ -50,7 +50,17 @@ def _get_value(context, key):
         # (e.g. catching KeyError).
         if key in context:
             return context[key]
-    elif type(context).__module__ != _BUILTIN_MODULE:
+    if isinstance(context, list):
+        # If we're dealing with a list or a list subclass attempt to use the key
+        # as an index on the list.
+        #
+        # We pass on ValueError (the key is not an int) or IndexError (the key/int
+        # is not in the list). And continue with normal processing.
+        try:
+            return context[int(key)]
+        except (ValueError, IndexError):
+            pass
+    if type(context).__module__ != _BUILTIN_MODULE:
         # Then we consider the argument an "object" for the purposes of
         # the spec.
         #

pystache/tests/test_context.py

@@ -221,6 +221,12 @@ class MyList(list): pass
         self.assertEqual(_get_value(item1, 'pop'), 2)
         self.assertNotFound(item2, 'pop')
 
+        # get list items by index
+        self.assertEqual(_get_value(item2, '0'), 1)
+
+        # Don't throw errors if we pass a non-int to a list.
+        self.assertNotFound(item2, 'numberone')
+
 
 class ContextStackTestCase(unittest.TestCase, AssertIsMixin, AssertStringMixin,
                            AssertExceptionMixin):
@@ -497,3 +503,10 @@ def bar(self):
 
         stack = ContextStack({"foo": Foo()})
         self.assertEqual(stack.get(name), "Baz")
+
+    def test_dot_notation__list(self):
+        name = "foo.1"
+
+        # When any element in the path is callable, it should be automatically invoked
+        stack = ContextStack({"foo": ['Ignore me.', 'Choose me!']})
+        self.assertEqual(stack.get(name), "Choose me!")