bpo-40066: [Enum] update str() and format() output

[ethanfurman]

https://bugs.python.org/issue40066

[AlexWaygood]

Omg, did not mean to close that at all — sorry!!

[sobolevn]

Thanks for your work! Enums' text representation looks way better now.

[AlexWaygood]

This change appears to be causing CI to fail on docs for unrelated PRs ☹️https://github.com/python/cpython/runs/4831439882?check_suite_focus=true

[AdamWill]

I'm curious: why does this define a __init__ for Enum which does nothing at all (just pass)?

It causes pylint to start throwing warnings about subclasses of Enum which have their own __init__ not calling super's __init__, which Python's own docs and examples don't say they should, and which of course would be pointless since it does nothing. I'm sending a PR for pylint to not emit this warning for subclasses of Enum, but I don't understand why the do-nothing __init__ was added at all.

[gryznar]

Is that inheritting correct where the values are changed to str?

[ethanfurman]

@gryznar Good question: only because the __new__ uses integers as the values, and the "value" on the assignment line is saved in the description attribute. Without the custom __new__ the enum creation would have failed, since strings are not integers.

[gryznar]

Is removing "{0}" proper?

[ethanfurman]

@gryznar Only because it was changed to %s later.