[Alex]

I added a method to datetimetester [1] to compute some overall statistics on tzfiles. My code ignores "version 2" data, so I include only transitions that fall within 32-bit time_t (1900 to 2038 range).

From staring at zic.c, looks like (so far) the data in the version 2 section is identical to that in the version 1 section, except written out in wider data formats. The pretty clear intent is that they never intend to generate explicit transitions beyond 2037 in any version, until it's after 2037 in the real world and they need to do so because a POSIX TZ rule can't handle some new goofy exception (and version 2 also contains a POSIX TZ rule at the end, when possible). Then they'll need to add new transitions in the version 2 section only (version 1 data formats are too narrow to record them).

I am considering making the cut-off at 1970 and assume 1970 standard time for all times before that year.

Is there a real need for a "high performance" tzinfo? That is, who cares? ;-) It would sure be _surprising_ if a Python wrapping of zoneinfo returned different results than native Linux tools wrapping the same thing.

I think this is best we can do on Windows

Of course not, if by "best" we mean "gets the same answers everyone else gets". In that case, "best" is returning what the IANA database says should be returned in all cases.

where (IIRC) mktime does not work for times before epoch. (What about localtime?)

Python 3.4.3 (v3.4.3:9b73f1c3e601, Feb 24 2015, 22:44:40) [MSC v.1600 64 bit (AMD64)] on win32

...

...

import time time.localtime(0) time.struct_time(tm_year=1969, tm_mon=12, tm_mday=31, tm_hour=18, tm_min=0, tm_sec=0, tm_wday=2, tm_yday=365, tm_isdst=0)

...

...

time.localtime(-1) Traceback (most recent call last): File "<pyshell#2>", line 1, in <module> time.localtime(-1) OSError: [Errno 22] Invalid argument

Which is another meaning for "best": avoid flaky C library functions altogether.

...

...

epoch = datetime(1970, 1, 1) epoch + timedelta(seconds=1e11) datetime.datetime(5138, 11, 16, 9, 46, 40) import time time.localtime(1e11) Traceback (most recent call last): File "<pyshell#13>", line 1, in <module> time.localtime(1e11) OSError: [Errno 22] Invalid argument