the template_filter now expects the parentheses

flask.py

@@ -640,24 +640,20 @@ class Flask(object):
             return f
         return decorator
 
-    def template_filter(self, arg=None):
+    def template_filter(self, name=None):
         """A decorator that is used to register custom template filter.
         You can specify a name for the filter, otherwise the function
         name will be used. Example::
 
-          @app.template_filter
+          @app.template_filter()
           def reverse(s):
               return s[::-1]
 
         :param name: the optional name of the filter, otherwise the
                      function name will be used.
         """
-        if type(arg) is types.FunctionType:
-            self.jinja_env.filters[arg.__name__] = arg
-            return arg
-
         def decorator(f):
-            self.jinja_env.filters[arg or f.__name__] = f
+            self.jinja_env.filters[name or f.__name__] = f
             return f
         return decorator
 

tests/flask_tests.py

@@ -311,16 +311,7 @@ class TemplatingTestCase(unittest.TestCase):
             macro = flask.get_template_attribute('_macro.html', 'hello')
             assert macro('World') == 'Hello World!'
 
-    def test_template_filter_not_called(self):
+    def test_template_filter(self):
-        app = flask.Flask(__name__)
-        @app.template_filter
-        def my_reverse(s):
-            return s[::-1]
-        assert 'my_reverse' in  app.jinja_env.filters.keys()
-        assert app.jinja_env.filters['my_reverse'] == my_reverse
-        assert app.jinja_env.filters['my_reverse']('abcd') == 'dcba'
-
-    def test_template_filter_called(self):
         app = flask.Flask(__name__)
         @app.template_filter()
         def my_reverse(s):