[Python-Dev] The new and improved PEP 572, same great taste with 75% less complexity! (original) (raw)

Tim Peters tim.peters at gmail.com
Thu Apr 26 12:58:32 EDT 2018

[Kirill Balunov <kirillbalunov at gmail.com>]

Not sure, but if additional motivating examples are required, there is a common pattern for dynamic attribute lookup (snippet from copy.py):

reductor = dispatchtable.get(cls) if reductor: rv = reductor(x) else: reductor = getattr(x, "reduceex", None) if reductor: rv = reductor(4) else: reductor = getattr(x, "reduce", None) if reductor: rv = reductor() else: raise Error("un(shallow)copyable object of type %s" % cls) which can with the current binding expression syntax simplified to: if reductor := dispatchtable.get(cls): rv = reductor(x) elif reductor := getattr(x, "reduceex", None): rv = reductor(4) elif reductor := getattr(x, "reduce", None): rv = reductor() else: raise Error("un(shallow)copyable object of type %s" % cls) which becomes much clearer, at least in my opinion. With kind regards, -gdg

Thanks for sharing that! While nobody else seems to, I absolutely love real code ;-)

This is effectively an instance of Guido's "if/elif/elif/elif/..." example template, where binding expressions shine. But actual real code can make a point viscerally that "consider stuff akin to the following semi-abstract pattern" can't.

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