> > ISO 8601 specifies dozens of ways to represent the same datetime
> 
> Yes, but not within the same format. If someone were to choose the 
> format '2014-04-10T24:00:00', they would have a reasonable expectation 
> that there is only one unique string that corresponds with that 
> datetime.

There are no format code in '2014-04-10T24:00:00', it cannot be a 
format. Without knowing the format, there is no way of telling what that 
string represents or whether it is a unique representation.

- Is the leading 0 in '04' mandatory or optional?
- Could the '00's be replaced by '0' or even left out altogether?
- Is 24:00:00 the exact same time as 00:00:00?
- If the final '00' represents seconds, does it accept microseconds '.000'?

> > As far as the inconsistency, I think that's an argument for being 
> > less strict, not more, and allowing non-ASCII digits in more places 
> > not just the first. Why shouldn't (let's say) a Bengali user specify 
> > the day of the month using Bengali digits?
> 
> That's an interesting direction. It might be a good thing to allow 
> users in different locales to specify datetime with their native 
> digits. But, if we were to go in that direction, we would have to:
> 
> 1. Define that use case more rigorously, consider whether it has any 
> effects we need to consider, like clashes with how the local culture 
> expresses dates.

I don't think so. Supporting different calendars is a seperate, and far 
more complex issue, than just supporting dumb transliteration of 
Hindu-Arabic digits 0...9 into other character sets.

This makes datetime behave more like int(), float(), etc, all of which 
accept non-ASCII digits including (e.g.) East-Asian double-width digits.

    py> int('５４３２')
    5432

Supporting non-Western calendars is a worthy thing, but probably best 
left for a third-party library.

> 2. Enable it in other fields except year.

That part is easy: replace `[0-9]` in regexes with `\d`.

> 3. Add tests for it. 

Aye, that would need to be done. Adding the tests would be the hard 
part.