[issue22547] Implement an informative `BoundArguments.__repr__`

[Yury Selivanov]

New submission from Yury Selivanov:

Can you propose a format for it?

I'm not sure that including all arguments and their reprs is a good idea, as it will make BA's repr too long.

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nosy: +yselivanov

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue22547>
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