[Python-ideas] Attribute-Getter Syntax Proposal

Benedikt Werner 1benediktwerner at gmail.com
Fri Mar 8 17:08:52 EST 2019

This was actually quite interesting to code, thanks for the idea Jonathan!

You can even support "magic.upper()" and "magic.real" at the same time 
as well as "magic[0]":

class MagicClass:
     NO_ARG = object()

     def __getattribute__(attr):
         def method(x=MagicClass.NO_ARG):
             if x is MagicClass.NO_ARG:
                 return lambda x: getattr(x, attr)()
             return getattr(x, attr)
         return method

     def __getitem__(attr):
         return lambda x: x[attr]

magic = MagicClass()

print(list(map(magic.upper(), ["abc", "def"])))  # ['ABC', 'DEF']
print(list(map(magic.real, [1j, 2, 3+4j])))      # [0.0, 2, 3.0]
print(list(map(magic[0], ["abc", "def"])))       # ['a', 'd']

You could also use None instead of that NO_ARG thingy, because you most 
likely won't want to get any attributes of None objects, but that 
wouldn't produce proper errors incase you do anyways.

With metaclasses you propably could also make it work directly on the 
class without the need of a magic instance.


Am 08.03.2019 um 19:07 schrieb Jonathan Fine:
> Hi Samuel
> Interesting idea, and certainly addresses a real problem, if you find
> yourself creating lots of lambda expressions. But in my first opinion,
> not so useful that it merits adding to the syntax of Python.
> (Even if I never use it, it puts an extra burden on me when scanning
> Python code. Something that used to look like a syntax error is now
> valid. That's more work for me.)
> However, you can already achieve something similar, and perhaps more
> expressive. It is possible to define an object 'magic' such that
>     fn = magic.upper
>     fn = lambda x: x.upper()
> are effectively equivalent.
> And this can be done now. No need for a PEP and a new version of
> Python. And available for those who have to use some fixed already
> existing Python versions.
> I hope you'd be interesting in coding this up yourself. I'd have a
> limited amount of time to help you, but it would put you on a good
> learning curve, for fundamentals of the Python object model.

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