bpo-33805: Improve error message of dataclasses.replace()

[corona10]

https://bugs.python.org/issue33805

[corona10]

@ericvsmith PTAL

[ericvsmith]

Thanks for the PR. See comments.

[ericvsmith]

I don't think it's worth adding this mapping and the new __str__ just for this one error message.

[ericvsmith]

For consistency with the rest of the code, please change '{f.name}' to {f.name!r}. Also, just hard-code InitVar in the message, since this message is only applicable with InitVars.

[ericvsmith]

The else is not needed.

[ericvsmith]

Please add a test that shows that an InitVar does work with replace(), and check that its value is used (probably via a __post_init__ method). Maybe something like:

def __post_init__(self, y):
   self.x *= y

or similar.

[ericvsmith]

I'd prefer "Improve error message of dataclasses.replace() when an InitVar is not specified".

[bedevere-bot]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

[corona10]

@ericvsmith
I have made the requested changes; please review again

[bedevere-bot]

Thanks for making the requested changes!

@ericvsmith: please review the changes made to this pull request.

[ericvsmith]

Thanks! Looks good.

I'm going to wait a few days before I merge this, because at this late date I don't want to put this in to 3.7.0, I'll wait for 3.7.1.

[miss-islington]

Thanks @corona10 for the PR, and @ericvsmith for merging it 🌮🎉.. I'm working now to backport this PR to: 3.7.
🐍🍒⛏🤖

[bedevere-bot]

GH-7876 is a backport of this pull request to the 3.7 branch.