Looking at pytz example, it's listed as YYYY.MM but that's not really right. You may also note the release history dates are not corresponding with months: https://pypi.org/project/pytz/#history
I emailed pytz maintainer directly, and it is actually based off of the IANA release files https://data.iana.org/time-zones/releases/ which use an incrementing letter suffix. That's not compatible for python version numbering, so pytz change it to an integer
e.g. Olson database 2018c (dated January, third Olson release in 2018) would correspond to pytz 2018.3
Looking at pytz example, it's listed as YYYY.MM but that's not really right. You may also note the release history dates are not corresponding with months: https://pypi.org/project/pytz/#history
I emailed pytz maintainer directly, and it is actually based off of the IANA release files https://data.iana.org/time-zones/releases/ which use an incrementing letter suffix. That's not compatible for python version numbering, so pytz change it to an integer
e.g. Olson database 2018c (dated January, third Olson release in 2018) would correspond to pytz 2018.3