[Datetime-SIG] PEP-495 - Strict Invalid Time Checking

[Carl Meyer]

On 08/25/2015 02:10 PM, Alexander Belopolsky wrote:
> 
> On Tue, Aug 25, 2015 at 3:36 PM, Carl Meyer <carl at oddbird.net
> <mailto:carl at oddbird.net>> wrote:
> 
>     Given the unlikelihood of someone trying to schedule an appointment at
>     2am, I didn't care much about the specific choice of user experience for
>     the DST gaps and folds; my overriding concerns were to a) not crash the
>     application when displaying a DST-transition day, and b) minimize the
>     harm done to my codebase (in fragility or added complexity) for the sake
>     of handling this rare edge case.
> 
> 
> Here is my recommendation for your case.  Assuming that taking user
> entry is equivalent to parsing date and time string in some format and
> scheduling is equivalent to writing a seconds since epoch timestamp into
> some database, do the following post-PEP 495:
> 
> dt = datetime.strptime(input, format)
> s = dt.timestamp()
> schedule(s)
> # optionally
> sdt = datetime.fromtimestamp(s)
> if dt != sdt:
>     warn("You specified an invalid time %s, we scheduled your
> appointment for %s", dt, sdt)
> 
> Instead of a warning, your program may highlight the changed hour in read.
> 
> This program will have no means of scheduling in the "fold=1" hour and
> will correct you if you enter time that falls in a gap.  The PEP 495
> design is motivated by precisely this type of application.

You are missing the crux of my use case, which is that I need to
generate a calendar to display to the user, with all the half-hour slots
from midnight to midnight for one day in it (and I need the actual
timezone-aware instants of the start and end time for each slot so that
I can properly populate its availability status based on a database
table of existing appointments, with start and end times stored in UTC).
So your solution, which is all about "taking user entry," is not
relevant to the use case.

Carl

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