Fixed groupby bare integer.  This fixes #40
diff --git a/jinja2/filters.py b/jinja2/filters.py
index 5b394de..1ef47f9 100644
--- a/jinja2/filters.py
+++ b/jinja2/filters.py
@@ -53,7 +53,7 @@
     passed object with the rules of the environment.  Dots are allowed
     to access attributes of attributes.
     """
-    if '.' not in attribute:
+    if not isinstance(attribute, basestring) or '.' not in attribute:
         return lambda x: environment.getitem(x, attribute)
     attribute = attribute.split('.')
     def attrgetter(item):
diff --git a/jinja2/testsuite/filters.py b/jinja2/testsuite/filters.py
index 5bb6b12..aefe768 100644
--- a/jinja2/testsuite/filters.py
+++ b/jinja2/testsuite/filters.py
@@ -288,6 +288,13 @@
             ""
         ]
 
+    def test_groupby_tuple_index(self):
+        tmpl = env.from_string('''
+        {%- for grouper, list in [('a', 1), ('a', 2), ('b', 1)]|groupby(0) -%}
+            {{ grouper }}{% for x in list %}:{{ x.1 }}{% endfor %}|
+        {%- endfor %}''')
+        assert tmpl.render() == 'a:1:2|b:1|'
+
     def test_groupby_multidot(self):
         class Date(object):
             def __init__(self, day, month, year):