On Mon, 4 Jun 2018 at 17:29, Ivan Pozdeev via Python-Dev <python-dev@python.org> wrote:

On 05.06.2018 3:09, Matthias Bussonnier wrote:

This may even be a bug/feature of IPython,

I see that inspect.signature(timedelta) fails, so if timedelta? says

Init signature: timedelta(self, /, *args, **kwargs)

Then this may be some IPython internal logic. The timedelta class seem to use __new__ instead of __init__ (not sure why)

Because it's an immutable type.

Ah, yes, thanks.

and __new__ have a meaningful signature,

So maybe we should fallback on that during signature inspection.

According to https://stackoverflow.com/questions/4374006/check-for-mutability-in-python ,
there are no reliable tests for mutability.

Sure, but we can test if the signature of __init__ is (self,/, *args, **kwargs), and if it is, it is useless we can attempt to get the signature from __new__ and show that instead. We do similar things for docstrings, if __init__ have no docstring we look at the class level docstring.