Message 409114 - Python tracker

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Author	Gobot1234
Recipients	Gobot1234, gvanrossum, kj
Date	2021-12-24.00:01:32
SpamBayes Score	-1.0
Marked as misclassified	Yes
Message-id	<1640304092.48.0.180382760459.issue46170@roundup.psfhosted.org>
In-reply-to

Content
I'd like to propose making the error message when subclassing typing.NewType much more understandable. Currently it looks like: ``` TypeError: NewType.__init__() takes 3 positional arguments but 4 were given ``` But I think we could do much better by adding __mro_entries__ to the class and then just having that raise a TypeError telling users they cannot subclass NewType and they are probably looking for `NewType('Subclass', OlderType)`. I'd be happy to patch this myself if this sounds like a good idea.

I'd like to propose making the error message when subclassing typing.NewType much more understandable. Currently it looks like:
```
TypeError: NewType.__init__() takes 3 positional arguments but 4 were given
```
But I think we could do much better by adding __mro_entries__ to the class and then just having that raise a TypeError telling users they cannot subclass NewType and they are probably looking for `NewType('Subclass', OlderType)`. I'd be happy to patch this myself if this sounds like a good idea.

History
Date	User	Action	Args
2021-12-24 00:01:32	Gobot1234	set	recipients: + Gobot1234, gvanrossum, kj
2021-12-24 00:01:32	Gobot1234	set	messageid: <1640304092.48.0.180382760459.issue46170@roundup.psfhosted.org>
2021-12-24 00:01:32	Gobot1234	link	issue46170 messages
2021-12-24 00:01:32	Gobot1234	create