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

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 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20180426/19239ea0/attachment-0001.html>

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