C:

https://github.com/python/cpython/blob/8b33961e4bc4020d8b2d5b949ad9d5c669300e89/Modules/_datetimemodule.c#L3183

pure python:

https://github.com/python/cpython/blob/8b33961e4bc4020d8b2d5b949ad9d5c669300e89/Lib/datetime.py#L927


this makes it difficult to properly type in mypy:

https://github.com/python/typeshed/blob/209b6bb127f61fe173a60776e23883ac450cf1c8/stdlib/2and3/datetime.pyi#L55

and calling with `.strftime(fmt=...)` or `.strftime(format=...)` is inconsistent

(that said, it should _probably_ be a positional-only argument)

I think a positional-only argument would be the best option if we could do it, but it would be a backwards-incompatible change and it's probably not worth the hassle.

If anyone is using the keyword argument, they're probably using `format=` rather than `fmt=`, since it's pretty rare for anyone to use the pure python version of datetime. PyPy uses it, but I think they tend to aim for consistency with the C API of CPython, and it seems like they already patch s/fmt/format/ themselves: https://foss.heptapod.net/pypy/pypy/-/blob/branch/default/lib_pypy/datetime.py#L781

If anyone wants to make a PR I think we can fix this for 3.10, though unfortunately because it is an API change it can't be backported. I think in typeshed they can safely change from `fmt` to `format` even today (which would almost certainly be more accurate to end user use cases).

awesome, I'm going to work through this with someone in my discord as a demo / mentorship opportunity -- hope that's ok!

Updating this issue to cover the problem in date, time and datetime.

Ref https://github.com/python/typeshed/pull/6317 for a discussion about this in typeshed.

In addition to `date.strftime` and `time.strftime`, there is also a discrepancy in `datetime.fromtimestamp`. In the C implementation, the first parameter is called "timestamp"; in the pure-Python implementation, the first parameter is called "t".