Protocols in Python

Structural typing: duck typing the type checker understands.

from typing import Protocol


class Drawable(Protocol):
    def draw(self) -> str: ...


class Circle:
    def draw(self) -> str:
        return "( )"


class Square:
    def draw(self) -> str:
        return "[ ]"


def render(shapes: list[Drawable]) -> str:
    return " ".join(s.draw() for s in shapes)

How it works

1. A Protocol lists the methods a type must have.
2. Circle and Square match it without inheriting.
3. render accepts anything shaped like Drawable.

Keywords and builtins used here

• Circle
• Drawable
• Square
• class
• def
• draw
• for
• list
• render
• return
• self
• str

The run, in numbers

Lines

19

Characters to type

273

Tokens

84

Three-star pace

105 tpm

At the three-star pace of 105 tokens a minute, this run takes about 48 seconds.

Type this snippet

Step 5 of 5 in Protocols & context managers, step 19 of 53 in Pythonic Python.

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