[Python-Dev] Examples for PEP 572 (original) (raw)

Kirill Balunov kirillbalunov at gmail.com
Wed Jul 4 13:58:36 EDT 2018

Forwarding the reply to the list. Accidentally pressed the wrong button and sent this message personally to Serhiy. Sorry :)

ср, 4 июл. 2018 г. в 11:57, Serhiy Storchaka <storchaka at gmail.com>:

> 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)

I was going to rewrite this code as reductor = dispatchtable.get(cls) if reductor: rv = reductor(x) else: rv = x.reduceex(4) There were reasons for the current complex code in Python 2, but now classic classes are gone, and every class has the reduceex method which by default calls reduce which by default is inherited from object. With that simplification the benefit of using ":=" in this example looks less impressed. Yes you are right with this particular snippet (in its current version, it is an echo from Python 2). But I think you have missed the general idea: The logic of this code is flat (like a switch) but the visual structure is pretty nested. That is why (maybe just for me) there is a mental imbalance in perception. And this type of code is rather common. Therefore, for me, the main gain from using the assignment expression in these patterns of code is that the visual syntax emphasizes the semantics. To be honest, I do not see any benefit of usage of assignment expression outside if and while headers, but if others do see let it be so.

With kind regards, -gdg -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20180704/5ff45c57/attachment-0001.html>

More information about the Python-Dev mailing list