What is typing.Protocol?

Question

Accepted Answer

**Protocol** — structural typing (duck typing).

```python
from typing import Protocol, runtime_checkable

@runtime_checkable
class Drawable(Protocol):
    def draw(self) -> None: ...

class Circle:
    def draw(self) -> None:
        print("Drawing circle")

class Square:
    def draw(self) -> None:
        print("Drawing square")

# Function accepts any object with draw()
def render(shape: Drawable) -> None:
    shape.draw()

render(Circle())  # OK!
render(Square())  # OK!

# Type checking
print(isinstance(Circle(), Drawable))  # True

# Properties
class Comparable(Protocol):
    def __lt__(self, other: "Comparable") -> bool: ...

def sort(items: list[Comparable]) -> list[Comparable]:
    return sorted(items)
```

**Advantages:**
- Structural typing.
- No inheritance.
- Easier to test.

Python: What is typing.Protocol?