What does self(variable) do in Python?

Question

I'm trying to understand someone else's code in Python and I stumbled across a line I don't quite understand and which I can't find on the internet:

x=self(k)

with k being a torch-array. I know what self.something does but I haven't seen self(something) before.

This means that self is callable, indicating that this class may implement __call__ magic method. — Mechanic Pig
– Mechanic Pig, Commented Sep 6, 2022 at 16:57
If self is within a nn.Module, then this calls the containing class's forward method (which is invoked from __call__ as @MechanicPig points out). — erip
– erip, Commented Sep 6, 2022 at 16:58

Silvio Mayolo · Accepted Answer · 2022-09-06 16:59:03Z

3

self, for these purposes, is just a variable like any other, and when we call a variable with parentheses, it invokes the __call__ magic method. So

x = self(k)

is effectively a shortcut for

x = self.__call__(k)

Footnote: I say "effectively", because it's really more like

x = type(self).__call__(self, k)

due to the way magic methods work. This difference shouldn't matter unless you're doing funny things with singleton objects, though.

answered Sep 6, 2022 at 16:59

Silvio Mayolo

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