Inheriting from Protocols in Python

Question

Are there any benefits in inheriting from Protocols in Python?

eg.

class SampleProtocol(Protocol):
    def do_something(self) -> int:
      ...
    
class Sample(SampleProtocol):
    def do_something(self) -> int:
        return 10

or should Sample just be a class that implements the Protocol without explicitly inheriting from it?

Josiah · Accepted Answer · 2021-06-09 12:32:04Z

11

Another advantage, according to the PEP, is

type checkers can statically verify that the class actually implements the protocol correctly.

That is, it can warn you if Sample doesn't have a conforming do_something method.

answered Jun 9, 2021 at 12:32

Josiah

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1 Comment

Silvio Mayolo Over a year ago

Exactly! If you intend that a class follow a particular protocol, then saying so in your code (a) is self-documenting for future readers of your code, and (b) allows the compiler to check that your intentions are met.

chepner · Accepted Answer · 2021-06-08 14:59:02Z

0

Sample can just implement the required method. There is no intent for the protocol to be part of a class's MRO; it is for static type-checking only.

answered Jun 8, 2021 at 14:59

chepner

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2 Comments

Tyfingr Over a year ago

python.org/dev/peps/pep-0544/… looking at the pep it looks like it's a solid way of using protocols.

Albert Over a year ago

The question is not whether you can do it without inheritation, but the question is whether there are benefits in still using inheritation anyway. You do not really answer that.

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