PEP 572: Python assignment expressions has been accepted

Re:PEP 572: Python assignment expressions has been accepted by chriswarbo on Tuesday July 03, 2018 @03:23PM (#17452949)

Yeah, I had a feeling the real 'expansion' would be more involved. I didn't know about the lookup in __dict__, that's good to know.

I'm reminded of PHP, where (at least in version 5.*) we could write:

    $myObject->foo = function() { return "hello world"; };

    $x = $myObject->foo;
    $x(); // Hello world

    $myObject->foo();  // Error: no such method 'foo'

(Taken from an old comment https://news.ycombinator.com/item?id=8119419 )

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Re:PEP 572: Python assignment expressions has been accepted by bilboa on Tuesday July 03, 2018 @05:28PM (#17453736)

I found the official docs on how python special methods are looked up.

https://docs.python.org/3/reference/datamodel.html#special-l...

Apparently the runtime is even more picky than I showed. The method has to be defined on the object's type, not in the object's instance dictionary. So, really the lookup is something like:

  if hasattr(type(a), '__add__'):

The link I provided explains the rationale for bypassing the instance dictionary and `__getattribute__` method.

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