Latest x releases: version sorting broken

[miicha]

For some packages the version sorting of the x last relases does not work which leads to not fetching any versions.

This is caused by a problem of the version parsing in packaging.version. It usually works but the regex does not match arbitrary letters.
The problem was observed in the pytz package: versions 2004a, 2004b, 2004b.2 are pased correctly but 2004d raises an error.
Additionally the filtering is done in a large try ... except block that silently ignores the error in the on_error function which made debugging necessary.

        elif isinstance(exception, TypeError) or isinstance(exception, ValueError):
            # This occurs for testing or when todolist is corrupt
            pass

The problem could be mitigated by implementing #1433.

[cooperlees]

I don't believe that is PEP440 valid versioning, so due to that I don't expect bandersnatch to support it cleanly.

[miicha]

That is very likely. Nevertheless, it is a blocking issue for me to setup a mirror, because there are ~20 required packages that are not downloaded due to this issue (and stay on the todo list). For me the sort_by = time would be sufficient, so feel free to close this entry after merging PR #1594.

[cooperlees]

Won't support outside PEP440 ...