string representation of a timedelta objects cannot be read by time class

[lenneman]

Feature or enhancement

Proposal:

The __str__ method of the datetime.timediff class returns a string representation of a time difference in days, hours, minutes, seconds, microseconds. The representation of minutes and seconds is with a leading zero, which is fine. But the hours is not with a leading zero.
Example:

>>> tstart = datetime.now()
...
>>> tend = datetime.now()
>>> tend - tstart
datetime.timedelta(seconds=5, microseconds=737300)
>>> str(tend - tstart)
'0:00:05.737300'

The problem is now that the method fromisoformat of the datetime.time class does not recognize this string as a valid iso-format string because of the missing leading zero:

>>> str(tend-tstart)
'0:00:05.737300'
>>> time.fromisoformat(str(tend-tstart))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: Invalid isoformat string: '0:00:05.737300'

adding a leading zero works:

>>> time.fromisoformat('00:00:05.737300')
datetime.time(0, 0, 5, 737300)
>>> str(time.fromisoformat('00:00:05.737300'))
'00:00:05.737300'

interestingly the __str__ method of time has a leading zero for the hours.

So the __str__ method of timedelta shall add a leading zero as well to be conform to the ISO format.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

[terryjreedy]

Seems sensible. Do you wish to a PR? Comparing the 2 __str__ methods, assuming in Python, should make this easy.

[lenneman]

I've no experience doing a PR, so I would prefer someone else does it.

[vstinner]

Changing datetime.timedelta.__str__() can break a lot of projects. I would prefer to add a datetime.timedelta.isoformat() function.

[StanFromIreland]

This will require changing the C implementation too I'm afraid.

@vstinner That issue has also had quite a lot of extensive discussion before:

• Add to/from string methods to datetime.timedelta #85426
• isoformat() / fromisoformat() for datetime.timedelta #86260

[serhiy-storchaka]

time and timedelta different types that represent different entities. They are not expected to have interoperable string representation.

>>> str(timedelta(seconds=1000000))
'11 days, 13:46:40'

As for adding methods to convert the string representation back to timedelta, there are already existing issues.