Use Self return type for the 'replace()' methods in datetime classes

[mzagozen]

Since Python 3.6, the replace() methods support subclasses - the return
type is the subclass being replaced.

Link to Python issue: https://bugs.python.org/issue31222

[srittau]

Thanks, you still need to annotate self with Self, as this is currently simply a type var, not typing.Self from PEP 673.

[mzagozen]

Thanks, you still need to annotate self with Self, as this is currently simply a type var, not typing.Self from PEP 673.

@srittau I just noticed my editor was giving me the same error🤦

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

pandas (https://github.com/pandas-dev/pandas)
+ pandas/_libs/tslibs/timestamps.pyi:116: error: Return type "datetime" of "replace" incompatible with return type "Timestamp" in supertype "datetime"  [override]
+ pandas/_libs/tslibs/timestamps.pyi:116: error: Signature of "replace" incompatible with supertype "date"  [override]
+ pandas/_libs/tslibs/timestamps.pyi:116: note:      Superclass:
+ pandas/_libs/tslibs/timestamps.pyi:116: note:          def replace(self, year: int = ..., month: int = ..., day: int = ...) -> Timestamp
+ pandas/_libs/tslibs/timestamps.pyi:116: note:      Subclass:
+ pandas/_libs/tslibs/timestamps.pyi:116: note:          def replace(self, year: int = ..., month: int = ..., day: int = ..., hour: int = ..., minute: int = ..., second: int = ..., microsecond: int = ..., tzinfo: Optional[tzinfo] = ..., fold: int = ...) -> datetime

[mzagozen]

This mypy_primer robot is pretty neat. I guess I should now make the equivalent PR in the pandas repo to fix https://github.com/pandas-dev/pandas/blob/main/pandas/_libs/tslibs/timestamps.pyi#L116?

[JelleZijlstra]

This mypy_primer robot is pretty neat. I guess I should now make the equivalent PR in the pandas repo to fix https://github.com/pandas-dev/pandas/blob/main/pandas/_libs/tslibs/timestamps.pyi#L116?

That would be great, but it's not required. We use the tool to get a sense of the impact of changes, and sometimes we decide new errors are acceptable and the library will have to fix them.

[Akuli]

The version checks shouldn't be necessary, because we no longer support Python 3.5.

[srittau]

@Akuli Good catch, #7602.