The HTTPClientError class is accessible via the paste.httpexceptions module.
This is an error condition in which the client is presumed to be in-error. This is an expected problem, and thus is not considered a bug. A server-side traceback is not warranted. Unless specialized, this is a '400 Bad Request'
'The server could not comply with the request since\r\nit is either malformed or otherwise incorrect.\r\n'
This exception as a WSGI application
See the source for more information.