[Python-ideas] Making datetime __str__ and isoformat more consistent

[MRAB]

On 02/11/2013 19:43, Ethan Furman wrote:
> On 11/02/2013 02:25 AM, Nick Coghlan wrote:
>> On 2 November 2013 12:49, MRAB <python at mrabarnett.plus.com> wrote:
>>> On 02/11/2013 02:17, Alexander Belopolsky wrote: +1
>>>
>>> Guaranteeing round-trip does seem like a reasonable behaviour to
>>> me.
>>
>> It's been a while since I had to deal seriously with date parsing,
>> but at the time, emitting microseconds was a fairly surefire way to
>> break most utilities that nominally supported date parsing.
>> Roundtripping is good, but interoperability is important too, and
>> as far as I am aware, microsecond support when parsing is still
>> sketchy with many date parsing tools.
>>
>> Ensuring that emitting and consuming microseconds is easy would
>> definitely be a good thing, but unless general date parsing
>> support (not just in Python, but in programming utilities in
>> general) has improved more dramatically in recent years than I
>> believe it has, emitting microseconds by default would be a
>> backwards compatibility breach.
>
> The thread seems to be leaning towards leaving the current __str__
> behavior as-is, and simply adding enough smarts to __new__ to be able
> to reconvert back to a date/datetime instance (whether or not
> microseconds have been emitted).
>
The OP was using strptime, so perhaps the simplest solution would be to
allow its 'format' argument to default to None, which would mean ISO
format with optional microseconds.