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mpkocher opened this issue Jun 5, 2025 · 3 comments
Open

Add __replace__ protocol support to timedelta #135195

mpkocher opened this issue Jun 5, 2025 · 3 comments
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type-feature A feature request or enhancement

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@mpkocher
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mpkocher commented Jun 5, 2025 •
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Feature or enhancement

Proposal:

Requirements:

  • Add __replace__ support for timedelta
  • Add .replace() to timedelta to be consistent with date and datetime

Currently, both date and datetime have a .replace() method and supports the __replace__ protocol

For unclear reasons, timedelta doesn't follow suit.

In [1]: from datetime import datetime, date, timedelta

In [2]: d = datetime.now()

In [3]: d.replace(day=1)
Out[3]: datetime.datetime(2025, 6, 1, 16, 50, 54, 282957)

In [4]: import copy

In [6]: copy.replace(d, second=1)
Out[6]: datetime.datetime(2025, 6, 5, 16, 50, 1, 282957)

In [7]: d = date.today()

In [8]: d.replace(day=1)
Out[8]: datetime.date(2025, 6, 1)

In [10]: copy.replace(d, day=1)
Out[10]: datetime.date(2025, 6, 1)

In [11]: t = timedelta(seconds=100)

In [12]: copy.replace(t, second=1)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[12], line 1
----> 1 copy.replace(t, second=1)

File ~/miniconda3/envs/core-313/lib/python3.13/copy.py:305, in replace(obj, **changes)
    303 func = getattr(cls, '__replace__', None)
    304 if func is None:
--> 305     raise TypeError(f"replace() does not support {cls.__name__} objects")
    306 return func(obj, **changes)

TypeError: replace() does not support timedelta objects
# Add a code block here, if required

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

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@mpkocher mpkocher added the type-feature A feature request or enhancement label Jun 5, 2025
@vstinner
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vstinner commented Jun 6, 2025

It makes sense to add a replace() method and support the __replace__() protocol for datetime.timedelta.

@StanFromIreland
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I can implement, unless you want to @mpkocher ? And, @pganssle , any reasons to not implement?

@serhiy-storchaka
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It was not implemented because ambiguous semantic.

Let you have td = timedelta(minutes=5, seconds=102).

>>> from datetime import *
>>> td = timedelta(minutes=5, seconds=102)
>>> td
datetime.timedelta(seconds=402)

What should td.replace(seconds=250) return -- timedelta(minutes=5, seconds=250) or timedelta(seconds=250)? What should td.replace(minutes=3) return -- timedelta(minutes=3, seconds=102), timedelta(minutes=3, seconds=42) or timedelta(seconds=180)? If the last option is the answer in both cases, how does it differ from just using the timedelta constructor? And I haven't even touched on the issue of days and microseconds, which complicates things even more.

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@vstinner @mpkocher @serhiy-storchaka @StanFromIreland