This exception is raised because astimezone() ends up calling time.localtime() to determine the appropriate time zone. If the datetime object has a pre-epoch value, it passes a negative timestamp to time.localtime(). On Windows, time.localtime() does not accept values greater than 0 (more discussion in issue #35796).

This is the minimal code required to reproduce the error:

from datetime import datetime
datetime(1969, 1, 1).astimezone()

Without the ability to ascertain the time zone with localtime(), I'm not sure if the time zone can be accurately determined. It's not clear what the proper behavior is. Maybe raise a ValueError?

PEP 615 proposes to include the IANA tz database, which would negate the need for a system call. Should we wait for this PEP before fixing this issue? Thoughts?