[thomas-st]

Good idea with the regex, haven't tried it. That being said, you didn't take the time into account to construct a datetime object, let alone attach time zone information. ciso8601 supports time zones using pytz' FixedOffset and UTC classes, see https://github.com/elasticsales/ciso8601 for additional benchmarks. There's potential for further speedup by using a tzoffset subclass written in C, but in our cases all dates were UTC anyway and so we didn't need the time zone.