def does_show_ban(self, element):
return False<EOL>
element -- A lxml root ElementTree.Element

Intended to be overridden in subclasses. The default implementation
always returns False.

This method is only called when parse_as_html is True. The subclass can
use this method to process this element and decide whether the server
has banned the client.

The motivation for this functionality is this: Some HTTP servers, when
they deduce that the client is a robot, will return a "200 OK" status
code but in the body of the response they will place a message
indicating that the client has been banned. This same body will be
returned regardless of the URL requested. If the functionality provided
by this method did not exist then the Downloader would keep downloading
resources and storing them in the cache, not realizing that the
resources are useless since the bodies do not contain any useful
information.

If this method returns True then an Exception is raised by the
open_url method, with a message indicating the URL that was
being processed at the time. This means that the useless body will not
be stored in the cache.