classification
Title: Should we define complex.__complex__ and bytes.__bytes__?
Type: Stage:
Components: Versions: Python 3.11
process
Status: open Resolution:
Dependencies: Superseder:
Assigned To: Nosy List: ethan smith, gvanrossum, gyu-don, mark.dickinson, serhiy.storchaka, terry.reedy
Priority: normal Keywords:

Created on 2015-05-18 21:37 by gvanrossum, last changed 2021-06-09 21:13 by gvanrossum.

Messages (7)
msg243538 - (view) Author: Guido van Rossum (gvanrossum) * (Python committer) Date: 2015-05-18 21:37
The special methods __complex__ and __bytes__ are not present on the corresponding builtin types.  Compare this to __int__ and __float__, which do exist on int and float, respectively.  Should we add the eponymous methods to complex and bytes?

(This came up in the context of PEP 484: https://github.com/ambv/typehinting/issues/68#issuecomment-88130156 )
msg243842 - (view) Author: Terry J. Reedy (terry.reedy) * (Python committer) Date: 2015-05-22 18:01
To my understanding, the presence of int.__int__ and float.__float__ are implementation issues.  I presume that float(ob) just calls ob.__float__ without slowing down for an isinstance(ob, float) check.  Ditto for int(ob).  The processing for complex(args) and bytes(args) are more complex and currently neither call an eponyous method. Would either be improved if it did?

One difference between int and complex, for instance, that might account for the internal implementation difference is that the second argument of int can only be used with a string first argument, while the second argument of complex cannot be used with a string first argument, and must support multiplication by 1j.  So int.__int__(self) does not allow a second parameter and can (and does) just return self.
msg314623 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2018-03-29 00:03
The difference between __complex__ and __bytes__ on one side, and __int__ and __float__ on other side is that the latter have dedicated type slots while the former are just entries in the type's dict. Thus testing and calling __int__ and __float__ is much faster.
msg314630 - (view) Author: Guido van Rossum (gvanrossum) * (Python committer) Date: 2018-03-29 01:58
It's not necessary for complex() and bytes() to call the special methods if the argument's type is exactly complex or bytes (respectively) -- these cases are already taken care of by the current code.  But adding these special methods enables other code to be more regular, without having to test for the special cases.
msg389805 - (view) Author: Takumi Kato (gyu-don) Date: 2021-03-30 08:37
Recently, the situation has changed. We should consider this issue again.

typing.SupportsComplex is an ABC with one abstract method __complex__.
Thus, isinstance(complex, typing.SupportsComplex) is False.
typing.SupportsBytes also.

It is nonsense.
msg395471 - (view) Author: Ethan Smith (ethan smith) * Date: 2021-06-09 21:09
While I don't think it is nonsense, I do think it would be quite useful to add these. I just submitted PRs to typeshed and numpy adding complex to unions that already had SupportsComplex, because of the lack of __complex__. I'd be happy to work on a PR for this if it would be accepted.
msg395474 - (view) Author: Guido van Rossum (gvanrossum) * (Python committer) Date: 2021-06-09 21:13
Yeah, the more I think about it, the more it looks like we should add the special methods -- even if they won't necessarily be called *if the type is exactly 'complex' or 'bytes'*.

Now, until we've written and released the code we won't know for sure whether this might break somebody's corner case, so we should play it safe and only do this for 3.11 and make sure it's mentioned in the What's New.
History
Date User Action Args
2021-06-09 21:13:52gvanrossumsetmessages: + msg395474
versions: + Python 3.11, - Python 3.5
2021-06-09 21:09:21ethan smithsetnosy: + ethan smith
messages: + msg395471
2021-03-30 08:37:32gyu-donsetnosy: + gyu-don
messages: + msg389805
2018-03-29 15:25:14mark.dickinsonsetnosy: + mark.dickinson
2018-03-29 01:58:59gvanrossumsetmessages: + msg314630
2018-03-29 00:04:41serhiy.storchakalinkissue33055 superseder
2018-03-29 00:03:47serhiy.storchakasetnosy: + serhiy.storchaka
messages: + msg314623
2015-05-22 18:01:12terry.reedysetnosy: + terry.reedy
messages: + msg243842
2015-05-18 21:37:35gvanrossumcreate