[Python-ideas] Please reconsider the Boolean evaluation of midnight

[Bruce Leban]

On Wed, Mar 5, 2014 at 5:53 PM, Tim Peters <tim.peters at gmail.com> wrote:

> That's there because `utcoffset()` is defined to return minutes.
>

It returns either minutes *or a timedelta*:

datetime.utcoffset()¶<http://docs.python.org/2/library/datetime.html#datetime.datetime.utcoffset>

If tzinfo <http://docs.python.org/2/library/datetime.html#datetime.tzinfo>
is None, returns None, else returns self.tzinfo.utcoffset(self), and raises
an exception if the latter doesn't return None, or a
timedelta<http://docs.python.org/2/library/datetime.html#datetime.timedelta>
 object representing a whole number of minutes with magnitude less than one
day.


tzinfo.utcoffset(*self*, *dt*)

Return offset of local time from UTC, in minutes east of UTC. If local time
is west of UTC, this should be negative. Note that this is intended to be
the total offset from UTC; for example, if
atzinfo<http://docs.python.org/2/library/datetime.html#datetime.tzinfo>
object
represents both time zone and DST adjustments,
utcoffset()<http://docs.python.org/2/library/datetime.html#datetime.tzinfo.utcoffset>
should
return their sum. If the UTC offset isn't known, return None. Else the
value returned must be a
timedelta<http://docs.python.org/2/library/datetime.html#datetime.timedelta>object
specifying a whole number of minutes in the range -1439 to 1439 inclusive
(1440 = 24*60; the magnitude of the offset must be less than one day).

A
> rule is needed to specify how the naive time object and `utcoffset()`
> interact to define the result.
>

Not sure why you attach 'naive' to time. Time objects carry units with
them, unlike integers. I would say 'naive time value' in reference to an
integer.

Combining a time and an integer can be done by converting the time to
minutes (which is a bit confusing since in most contexts in this class,
minutes values are integers) or it can be done by interpreting the integer
utcoffset result as minutes (as it is documented).



> > Perhaps a reasonable improvement would be to change this to:
> >
> > a time object is considered to be true unless it represents exactly
> midnight
> > local time,
>

The above part is the key part of my suggested improvement. Reading the
current documentation, the fact that it means midnight local time is falsey
is not obvious.


--- Bruce
Learn how hackers think: http://j.mp/gruyere-security
https://www.linkedin.com/in/bruceleban
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