There are issues in implementing support of request rate in robotparser.

    req_rate = collections.namedtuple('req_rate',
                                      'requests seconds')
    entry.req_rate = req_rate
    entry.req_rate.requests = int(numbers[0])
    entry.req_rate.seconds = int(numbers[1])

First, a new namedtuple type is created for every entry. This is slow even with recent namedtuple optimizations, and is much slower in 3.6. This wastes a memory, since new type is created for every entry. This is definitely wrong, since req_rate is set to a namedtuple type instead of namedtuple instance. And there is a question why a namedtuple is used here at all. Other classes in this module are not namedtuples.