What is the `typing.Protocol` class?

Question

Accepted Answer

**Protocol** — structural subtyping (duck typing with type safety).

```python
from typing import Protocol

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")

# Any class with draw() works — no inheritance needed
def render(shape: Drawable) -> None:
    shape.draw()

render(Circle())  # OK
render(Square())  # OK
# render("text")  # Type error: str has no draw()
```

**vs ABC:**
- Protocol: structural typing (duck typing).
- ABC: nominal typing (explicit inheritance).
- Protocol: no inheritance required.
- ABC: must inherit from ABC.

**Use cases:**
- Type-checking duck-typed code.
- Third-party library compatibility.

Python: What is the `typing.Protocol` class?