[Python-Dev] PEP 495 accepted (original) (raw)
Alexander Belopolsky alexander.belopolsky at gmail.com
Tue Sep 22 16:55:50 CEST 2015
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On Tue, Sep 22, 2015 at 10:43 AM, Guido van Rossum <guido at python.org> wrote:
Based on the UTC/local diagram from the "Mind the Gap" section, am I
correct in thinking that the modified invariant that also covers times in a gap is:
dt == datetime.fromtimestamp(dt.astimezone(utc).astimezone(dt.tzinfo).timestamp()) That is, for local times that exist, the invariant "dt == dt.astimezone(utc).astimezone(dt.tzinfo)" holds, but for times that don't exist, "dt.astimezone(utc).astimezone(dt.tzinfo)" will normalise them to be a time that actually exists in the original time zone, and that normalisation also effectively happens when calling "dt.timestamp()". That can't be right -- There is no way any fromtimestamp() call can return a time in the gap.
I don't think Nick said that.
I think about the only useful invariant here is
dt.timestamp() == dt.astimezone(utc).timestamp() == dt.astimezone().timestamp()
Yes, this is just another way to say that .astimezone() conversions are now "lossless." -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20150922/238793e0/attachment.html>
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