[Python-Dev] Store timestamps as decimal.Decimal objects

[Victor Stinner]

> I think this is definitely worth elaborating in a PEP (to recap the
> long discussion in #11457 if nothing else).

The discussion in issues #13882 and #11457 already lists many
alternatives with their costs and benefits, but I can produce a PEP if
you need a summary.

> In particular, I'd want to
> see a very strong case being made for supporting multiple formats over
> standardising on a *single* new higher precision format (for example,
> using decimal.Decimal in conjunction with integration of Stefan's
> cdecimal work) that can then be converted to other formats (like
> datetime) via the appropriate APIs.

To convert a Decimal to a datetime object, we have already the
datetime.datetime.fromtimestamp() function (it converts Decimal to
float, but the function can be improved without touching its API). But
I like the possibility of getting the file modification time directly
as a datetime object to have something like:

>>> s=os.stat("setup.py", timestamp="datetime")
>>> print(s.st_atime - s.st_ctime)
52 days, 1:44:06.191293

We have already more than one timestamp format: os.stat() uses int or
float depending on os.stat_float_times() value. In 5 years, we may
prefer to use directly float128 instead of Decimal. I prefer to have
an extensible API to prepare future needs, even if we just add Decimal
today.

Hum, by the way, we need a "int" format for os.stat(), so
os.stat_float_times() can be deprecated. So there will be a minimum of
3 types:
 - int
 - float
 - decimal.Decimal

Victor