ENH: Implement round dunder methods for Timestamp and Timedelta

[Aloqeely]

• closes BUG: TypeError("type Timedelta doesn't define __round__ method") #58071
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

[Aloqeely]

pre-commit.ci autofix

[jbrockmendel]

Doesn’t the dunder method not take a freq keyword?

[Aloqeely]

You're right it doesn't, it instead takes ndigits which is not relevant here, so I thought for extra customizability I'll take freq in place of ndigits (same as NDFrame.__round__ which takes decimals instead of ndigits)

[Aloqeely]

But I have 1 question, should freq have a default value? as you would usually expect round(object) to work without any extra arguments, if so, what should the default value be?

[jbrockmendel]

I would not expect that to work

[Aloqeely]

Weirdly enough it does, for example:

In [1]: import pandas as pd
In [2]: td = pd.Timedelta(days=1, hours=2, minutes=34, seconds=56.78)
In [3]: round(td, "s")
Out[3]: Timedelta('1 days 02:34:57')
In [4]: round(td)
TypeError: __round__() takes exactly 2 positional arguments (1 given)

[Aloqeely]

Or were you replying to my last sentence when I said that I expect round(object) to work without any args

[jbrockmendel]

Or were you replying to my last sentence when I said that I expect round(object) to work without any args

That

[rhshadrach]

If this just happens to work due to an implementation detail in CPython, then it seems to me to be an abuse of the Python API and could break in the future. Is supporting other arguments in Python's round documented somewhere?

[asishm]

python round which is just object.__round__(self[, ndigits])

[mroeschke]

I don't think __round__ should be implemented for these objects. Since round is only well specified for numeric values, I think it's too opaque to apply for datelike objects.

[Aloqeely]

Makes sense, I apologize, I was too hasty to make a PR.
Should I close this and wait until a decision is made?

[mroeschke]

I would recommend closing this PR until discussion in the issue has resolved

[JustAnotherVeryNormalDeveloper]

I don't think __round__ should be implemented for these objects. Since round is only well specified for numeric values, I think it's too opaque to apply for datelike objects.

@mroeschke @MarcoGorelli @rhshadrach

Hello, I was the one that created the issue.

There is already an implementation of a round method for timedelta

pd.Timedelta.round('s') works. (https://pandas.pydata.org/docs/reference/api/pandas.Timedelta.round.html)
so round(pd.Timedelta) feel intuitive and just need to be added ?

(I'm going on again because I still use the fix I made here #58071 on my production server and I would be happy to not have to handle this manually but to see the library handle it).

[rhshadrach]

so round(pd.Timedelta) feel intuitive and just need to be added ?

As commented above (#58081 (comment)):

If this just happens to work due to an implementation detail in CPython, then it seems to me to be an abuse of the Python API and could break in the future.

Do you disagree that making round(pd.Timedelta) work as it's implemented in this PR is an abuse of the Python API?

Alternatively, if you are wanting the signature to be something like def __round__(self, n=None): and have the n mean seconds, then I am still of the opinion expressed in #58071 (comment) and quite negative on adding this.

[JustAnotherVeryNormalDeveloper]

So because round(td, n=5) isn't really clear, you don't want to implement round(td).
I understand your point of view.

I disagree that it's a good enough reason to not do it.
with or without this feature, round(td, n=5) would crash.
by doing this feature, hundreds/thousand of developers throughs ages would feel the library even more intuitive with round(td).
But the philosophical defense is understandable. It feels like the defense of a C++ dev rather than python dev but I understand.

Have a nice day boys and thanks for this library (I use it every day at work and I love it !<3)