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main.py

from typing import Iterable, Protocol
from dataclasses import dataclass


@dataclass
class Square:
    sidelength: float

    def area(self) -> float:
        return self.sidelength * self.sidelength


@dataclass
class Rectangle:
    wd: float
    ht: float

    def area(self) -> float:
        return self.wd * self.ht


class HasArea(Protocol):
    def area(self) -> float: ...


def sum_area(shapes: Iterable[HasArea]) -> float:
    return sum(s.area() for s in shapes)


print(sum_area([Rectangle(3, 4), Square(1)]))