> Finally, urllib/robotparser.py appears to contain a bug in the> following:>>   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])> > As I read it, this should fail as the req_rate is immutable.Ref:https://news.ycombinator.com/item?id=15136961They are mistaken in the nature of the bug, which is that req_rate isa namedtuple type, rather than an instance. As such, it is actuallymutable, causing the assignments to not fail. Every entry creates aseparate req_rate type, so it all works, but not in the way it should.

* The named tuple class should begin with a capital letter and be fully self-documenting: "RequestRate".* The creation of the named tuple class should be done only once, not on every call.  Instead only a new instance should be creating on every call:     entry.req_rate = req_rate(RequestRate)* There needs to be a test.* The docstring should be updated to include the name of the class refer to the term named tuple instead of the namedtuple() factory function:     - Returns the contents of the ``Request-rate`` parameter from     - ``robots.txt`` in the form of a :func:`~collections.namedtuple`     - ``(requests, seconds)``.  If there is no such parameter or it doesn't     + Returns the contents of the ``Request-rate`` parameter from     + ``robots.txt`` as a :term:`named tuple` ``RequestRate(requests, seconds)``.     + If there is no such parameter or it doesn't

Good catch and thank you for turning the bug report in the HN thread to a pull request! I agree with all of Raymond's comments.I have two more comments:* Please follow our commit style athttps://devguide.python.org/committing/#commit-messages* We need a NEWS entry. You can find details athttps://devguide.python.org/committing/#what-s-new-and-news-entries (we don't need to add an entry inDoc/whatsnew/ so you can safely ignore it)

There was a typo in my previous message.  The instantiation code should be:   entry.req_rate = RequestRate(int(numbers[0]), int(numbers[1]))

What is a reason of making req_rate a named tuple?

> What is a reason of making req_rate a named tuple?I don't know the original reason but it seems like a normal use of named tuples to make the data more self-describing to help with debugging and also to support field access by name, rr.requests or rr.seconds is clearer than rr[0] or rr[1].

This is a normal use of named tuples for adding access by name to tuple results. But req_rate never was a tuple. Nobody used rr[0].

There is no rule that something had to be a tuple at some point in its history before becoming a named tuple.  This use seems perfectly reasonable to me.

New changeset3df02dbc8e197053105f9dffeae40b04ec66766e by Raymond Hettinger (Berker Peksag) in branch 'master':bpo-31325: Fix usage of namedtuple in RobotFileParser.parse() (#4529)https://github.com/python/cpython/commit/3df02dbc8e197053105f9dffeae40b04ec66766e

New changesetff847d1ac7e6a8ee1fb6f8883cfb4aec4b4a9b03 by Raymond Hettinger (Miss Islington (bot)) in branch '3.6':bpo-31325: Fix usage of namedtuple in RobotFileParser.parse() (GH-4529) (#4533)https://github.com/python/cpython/commit/ff847d1ac7e6a8ee1fb6f8883cfb4aec4b4a9b03