Used "is" for comparisons with None.

django/core/mail/message.py

@@ -292,7 +292,8 @@ class EmailMessage(object):
         into the resulting message attachments.
         """
         if isinstance(filename, MIMEBase):
-            assert content == mimetype == None
+            assert content is None
+            assert mimetype is None
             self.attachments.append(filename)
         else:
             assert content is not None

django/forms/widgets.py

@@ -508,7 +508,7 @@ class Select(Widget):
         return mark_safe('\n'.join(output))
 
     def render_option(self, selected_choices, option_value, option_label):
-        if option_value == None:
+        if option_value is None:
             option_value = ''
         option_value = force_text(option_value)
         if option_value in selected_choices:

django/middleware/cache.py

@@ -96,7 +96,7 @@ class UpdateCacheMiddleware(object):
         # Control" header before reverting to using the default cache_timeout
         # length.
         timeout = get_max_age(response)
-        if timeout == None:
+        if timeout is None:
             timeout = self.cache_timeout
         elif timeout == 0:
             # max-age was set to 0, don't bother caching.

django/template/defaulttags.py

@@ -315,7 +315,7 @@ class RegroupNode(Node):
 
     def render(self, context):
         obj_list = self.target.resolve(context, True)
-        if obj_list == None:
+        if obj_list is None:
             # target variable wasn't found in context; fail silently.
             context[self.var_name] = []
             return ''

django/test/_doctest.py

@@ -1345,7 +1345,7 @@ class DocTestRunner:
                     # exception message will be in group(2)
                     m = re.match(r'(.*)\.(\w+:.+\s)', exc_msg)
                     # make sure there's a match
-                    if m != None:
+                    if m is not None:
                         f_name = m.group(1)
                         # check to see if m.group(1) contains the module name
                         if f_name == exception[0].__module__: