Getting "." from an empty context stack now raises a KeyNotFoundError.

pystache/context.py

@@ -14,6 +14,9 @@ spec, we define these categories mutually exclusively as follows:
 
 """
 
+from pystache.common import PystacheError
+
+
 # This equals '__builtin__' in Python 2 and 'builtins' in Python 3.
 _BUILTIN_MODULE = type(0).__module__
 
@@ -73,6 +76,21 @@ def _get_value(context, key):
     return _NOT_FOUND
 
 
+class KeyNotFoundError(PystacheError):
+
+    """
+    An exception raised when a key is not found in a context stack.
+
+    """
+
+    def __init__(self, key, details):
+        self.key = key
+        self.details = details
+
+    def __str__(self):
+        return "Key %s not found: %s" % (repr(self.key), self.details)
+
+
 class ContextStack(object):
 
     """
@@ -252,8 +270,10 @@ class ContextStack(object):
 
         """
         if name == '.':
-            # TODO: should we add a test case for an empty context stack?
-            return self.top()
+            try:
+                return self.top()
+            except IndexError:
+                raise KeyNotFoundError(".", "empty context stack")
 
         parts = name.split('.')
 

pystache/tests/test_context.py

@@ -8,10 +8,8 @@ Unit tests of context.py.
 from datetime import datetime
 import unittest
 
-from pystache.context import _NOT_FOUND
-from pystache.context import _get_value
-from pystache.context import ContextStack
-from pystache.tests.common import AssertIsMixin, AssertStringMixin, Attachable
+from pystache.context import _NOT_FOUND, _get_value, KeyNotFoundError, ContextStack
+from pystache.tests.common import AssertIsMixin, AssertStringMixin, AssertExceptionMixin, Attachable
 
 class SimpleObject(object):
 
@@ -39,7 +37,7 @@ class DictLike(object):
         return self._dict[key]
 
 
-class GetValueTests(unittest.TestCase, AssertIsMixin):
+class GetValueTestCase(unittest.TestCase, AssertIsMixin):
 
     """Test context._get_value()."""
 
@@ -224,7 +222,8 @@ class GetValueTests(unittest.TestCase, AssertIsMixin):
         self.assertNotFound(item2, 'pop')
 
 
-class ContextStackTests(unittest.TestCase, AssertIsMixin, AssertStringMixin):
+class ContextStackTestCase(unittest.TestCase, AssertIsMixin, AssertStringMixin,
+                           AssertExceptionMixin):
 
     """
     Test the ContextStack class.
@@ -326,6 +325,24 @@ class ContextStackTests(unittest.TestCase, AssertIsMixin, AssertStringMixin):
         context = ContextStack.create({'foo': 'bar'}, foo='buzz')
         self.assertEqual(context.get('foo'), 'buzz')
 
+    ## Test the get() method.
+
+    def test_get__single_dot(self):
+        """
+        Test getting a single dot (".").
+
+        """
+        context = ContextStack("a", "b")
+        self.assertEqual(context.get("."), "b")
+
+    def test_get__single_dot__missing(self):
+        """
+        Test getting a single dot (".") with an empty context stack.
+
+        """
+        context = ContextStack()
+        self.assertException(KeyNotFoundError, "Key '.' not found: empty context stack", context.get, ".", "b")
+
     def test_get__key_present(self):
         """
         Test getting a key.