[issue5094] datetime lacks concrete tzinfo impl. for UTC

[Mark Dickinson]

Mark Dickinson <dickinsm at gmail.com> added the comment:

Some comments from playing with this patch (without having looked at the implementation):

- As noted above, the 'timezone' class can't be subclassed.  Is this deliberate?  I notice that Brett said "let users subclass as needed to add DST support" in msg107008.

- If I try to do  timezone(timedelta(hours=24)), I get an error message:
"ValueError: offset must be a timedelta between timedelta(1) and -timedelta(1)." and I have to think for a bit to remember that 'timedelta(1)' means 'timedelta(days=1)'.  Any chance of making this more explicit:  e.g. "between timedelta(hours=-24) and timedelta(hours=24)"?

- The existing docs say, at one point: "if utcoffset does not return None,
dst() should not return None either."  And yet it seems that this is exactly what happens for timezone instances:  utcoffset doesn't return None, but dst does.  Was there a reason for the explicit restriction in the docs, and are we sure that that reason is no longer valid?

- I find it strange that mytimezone.utcoffset(1+3j) works;  similarly for tzname and dst.  Perhaps it should be checked at least that the argument is a datetime.  Similarly for tzname and dst.

- And it also seems clunky that an argument *has* to be supplied for utcoffset, tzname and dst, only to be ignored.  Would it be possible to make the argument optional?

- Any chance of a nice __str__ implementation for timezone instances?  (And/or possibly a nice __repr__ as well)?

- The docs for tzname are misleading:  they claim that the default name has the form "UTCsHHMM".  This isn't true for UTC+0, whose name seems to be just "UTC".  It actually wouldn't seem unreasonable to have this print as "UTC+0000", just for consistency (and for ease of parsing for anyone on the receiving end of such a string).  Or the docs could be fixed.

- I'm very confused about utcoffset:  why can't I supply a UTC datetime (i.e. an aware datetime with tzinfo = timezone.utc) to this?  I suspect I'm misunderstanding something here...

- In the docs, replace "timezeone" with "timezone"

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<http://bugs.python.org/issue5094>
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