[issue18652] Add itertools.coalesce

[Mark Dickinson]

Mark Dickinson added the comment:

[Nick]
> Regarding the key parameter name, I believe this is closer to
> itertools.groupby ...

Isn't this mostly about the return type?  `pred` is an indication that a boolean is being returned (or that the return value will be interpreted in a boolean context), while `key` is used for more general transformations.  In that sense, `pred` makes more sense here.

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nosy: +mark.dickinson

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<http://bugs.python.org/issue18652>
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