parse_duration() ISO string sign is ignored when the timedelta only has days

[Hanno]

I'm pretty sure that this is a bug even though I'm not an expert on the ISO 8601 standard. The sign of a timedelta string will be ignored by django.utils.dateparse.parse_duration if the input string only contains days. Compare the following (notice the minus signs):

In [4]: timedelta(days=-1)
Out[4]: datetime.timedelta(days=-1)

In [5]: td = timedelta(days=-1)

In [6]: duration_iso_string(td)
Out[6]: '-P1DT00H00M00S'

In [7]: parse_duration(duration_iso_string(td))
Out[7]: datetime.timedelta(days=1)  # <-- Why is this 1 and not -1?

In [8]: td = timedelta(days=-1, microseconds=1)

In [9]: duration_iso_string(td)
Out[9]: '-P0DT23H59M59.999999S'

In [10]: parse_duration(duration_iso_string(td))
Out[10]: datetime.timedelta(days=-1, microseconds=1)

I guess the problem is in django/utils/dateparse.py line 147 that reads return days + sign * datetime.timedelta(**kw).
However, if datetime.timedelta(**kw) ends up being zero (timedelta(0)) then the sign multiplication ends up in zero, not -0. This is just a preliminary quick look though and maybe the problem is something else.

[Mariusz Felisiak]

Great catch. Would you like to prepare a patch?

[Hanno]

I can try! Hopefully I can find the time.

[Mariusz Felisiak]

​PR

[Mariusz Felisiak <felisiak.mariusz@…>]

In 2a76f43:

Fixed #32269 -- Fixed parse_duration() for negative days in ISO 8601 format.