The versioning relationship between pytz and the IANA Time Zone Database
pytz is a Python library that provides the world timezone database. pytz tracks the IANA Time Zone Database, though its version numbers don’t exactly match. For instance, pytz 2016.6.1 corresponds to the 2016f IANA Time Zone Database release. How does this work?
The IANA Time Zone Database’s versioning follows the pattern of yearX, where X is a letter incremented for every update in that year. Thus, 2016a is the first release of the year, and 2016f is the sixth.
pytz’s versioning is similar, but follows the Semantic Versioning convention of major.minor.patch
by tagging versions as year.num[.patch], where num is X above, but converted to a number starting at 1.
num = ord(X) - ord('a') + 1. Though IANA’s versioning increases consecutively,
pytz does not necessarily have a release for every IANA database version, so there can be gaps.
pytz was originally versioned exactly the same as the IANA database, but, in order to be compatible with pip, switched to the current scheme starting with 2013f / 2016.6.