[Python-Dev] Aware datetime from naive local time Was: Status on PEP-431 Timezones

[Alexander Belopolsky]

On Mon, Apr 13, 2015 at 2:05 PM, Chris Barker <chris.barker at noaa.gov> wrote:

> However, different UTC times may map to the same wall time and some
>> expressible wall times are not results of a map of any UTC time.
>>
>
> got it. I suggest you perhaps word it something like:
>
> wall_time = f( location, utc_time)
>
> and
>
> utc_time = f( location, utc_time )
>
> These are two different problems, and one is much harder than the other!
> (though both are ugly!)
>

You probably meant "utc_time = f( location, wall_time)" in the last
equation, but that would still be wrong.
A somewhat more correct equation would be

utc_time = f^(-1)( location, wall_time)

where f^(-1) is the inverse function of f, but since f in not monotonic, no
such inverse exists.

Finding the inverse of f is the same as solving the equation f(x) = y for
any given y.  If f is such that this
equation has only one solution for all possible values of y then an inverse
exists, but this
is not so in our case.
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