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

Kirill Balunov kirillbalunov at gmail.com
Thu Apr 26 09:27:18 EDT 2018 
2018-04-24 18:31 GMT+03:00 Chris Angelico <rosuav at gmail.com>:

>
> Recommended use-cases
> =====================
>
> [...]
>
>     # Capturing regular expression match objects
>     # See, for instance, Lib/pydoc.py, which uses a multiline spelling
>     # of this effect
>     if match := re.search(pat, text):
>         print("Found:", match.group(0))
>
>

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

    reductor = dispatch_table.get(cls)
    if reductor:
        rv = reductor(x)
    else:
        reductor = getattr(x, "__reduce_ex__", 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 := dispatch_table.get(cls):
        rv = reductor(x)
    elif reductor := getattr(x, "__reduce_ex__", 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
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