'Delete a cookie.  Fails silently if key doesn\'t exist.
:param key: the key (name) of the cookie to be deleted.
:param path: if the cookie that should be deleted was limited to a
path, the path has to be defined here.
:param domain: if the cookie that should be deleted was limited to a
domain, that domain has to be defined here.'

def delete_cookie(self, key, path='/', domain=None):

    self.set_cookie(key, expires=0, max_age=0, path=path, domain=domain)
