bpo-43869: Time Epoch is the same on all platforms

[vstinner]

Add an explicit test_epoch() test in test_time.

https://bugs.python.org/issue43869

[vstinner]

The Python test suite checks that the Epoch is 1970-01-01 at 00:00 since 2008! It's tested indirectly by test_structseq since this change:

commit 9c2019632b9e775dcc8ae259b5028f9824265c6a
Author: Christian Heimes <[email protected]>
Date:   Mon Jan 14 03:33:52 2008 +0000

    Added new an better structseq representation. E.g. repr(time.gmtime(0)) now returns 'time.struct_time(tm_year=1970, tm_mon=1, tm_mday=1, tm_hour=0, tm_min=0, tm_sec=0, tm_wday=3, tm_yday=1, tm_isdst=0)' instead of '(1970, 1, 1, 0, 0, 0, 3, 1, 0)'. The feature is part of #1816: sys.flags

Test:

    def test_repr(self):
        (...)
        t = time.gmtime(0)
        self.assertEqual(repr(t),
            "time.struct_time(tm_year=1970, tm_mon=1, tm_mday=1, tm_hour=0, "
            "tm_min=0, tm_sec=0, tm_wday=3, tm_yday=1, tm_isdst=0)")

[vstinner]

We could test more members, but I don't think that it is worth it. It can make the test more fragile if the exact value changes depending on the platform.

[iritkatriel]

This reads a bit strange now - you tell us exactly what the epoch is, and then tell us how to find out what it is. How about changing the above 3 lines to something like:

• The :dfn:epoch is the point where the time starts, the
  return value of time.gmtime(0).
  It is January 1, 1970, 00:00:00 (UTC) on all platforms.

[vstinner]

I agree that the doc sounds strange. But I wanted to keep "gmtime(0)", it sounds important to me. I like your wording, I copied it in my PR ;-) Would you mind to review it again?

[vstinner]

Thanks for the suggestion Irit, and thanks for the review Irit and Paul ;-)

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 FreeBSD Shared 3.x has failed when building commit a847785.

What do you need to do:

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3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/483/builds/1513) and take a look at the build logs.
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5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

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Summary of the results of the build (if available):

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remote: Enumerating objects: 13, done.        
remote: Counting objects:   8% (1/12)        
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remote: Counting objects: 100% (12/12)        
remote: Counting objects: 100% (12/12), done.        
remote: Compressing objects:  25% (1/4)        
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remote: Compressing objects:  75% (3/4)        
remote: Compressing objects: 100% (4/4)        
remote: Compressing objects: 100% (4/4), done.        
remote: Total 13 (delta 8), reused 8 (delta 8), pack-reused 1        
From https://github.com/python/cpython
 * branch                  main       -> FETCH_HEAD
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See "git help gc" for manual housekeeping.
rror: cannot lock ref 'refs/remotes/origin/HEAD': Unable to create '/usr/home/buildbot/python/3.x.koobs-freebsd-564d/build/.git/refs/remotes/origin/HEAD.lock': File exists.

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fatal: failed to run reflog
rror: task 'gc' failed
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HEAD is now at a847785b40   [bpo-43869](https://bugs.python.org/issue43869): Time Epoch is the same on all platforms (GH-30664)
Switched to and reset branch 'main'

4 errors

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