Merge pull request #549 from realpython/python-protocol

Sample code for the article on Python protocols

Author: brendaweles

python-protocol/README.md

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+# Python Protocols: Leveraging Structural Subtyping
+
+This folder provides the code examples for the Real Python tutorial [Python Protocols: Leveraging Structural Subtyping](https://realpython.com/python-protocol/).

python-protocol/adder_v1.py

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+from typing import Protocol
+
+
+class Adder(Protocol):
+    def add(self, x, y): ...
+
+
+class IntAdder:
+    def add(self, x, y):
+        return x + y
+
+
+class FloatAdder:
+    def add(self, x, y):
+        return x + y
+
+
+def add(adder: Adder) -> None:
+    print(adder.add(2, 3))
+
+
+add(IntAdder())
+add(FloatAdder())
+
+
+for adder in [IntAdder(), FloatAdder()]:
+    add(adder)

python-protocol/adder_v2.py

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+from typing import Protocol
+
+
+class Adder(Protocol):
+    def add(self, x: float, y: float) -> float: ...
+
+
+class IntAdder:
+    def add(self, x: int, y: int) -> int:
+        return x + y
+
+
+def add(adder: Adder) -> None:
+    print(adder.add(2, 3))
+
+
+# add(IntAdder())

python-protocol/adder_v3.py

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+from typing import Protocol
+
+
+class Adder(Protocol):
+    def add(self, x: int | float, y: int | float) -> int | float: ...
+
+
+class IntAdder:
+    def add(self, x: int, y: int) -> int:
+        return x + y
+
+
+def add(adder: Adder) -> None:
+    print(adder.add(2, 3))
+
+
+# add(IntAdder())

python-protocol/adder_v4.py

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+from typing import Protocol, TypeVar
+
+T = TypeVar("T", bound=int | float)
+
+
+class Adder(Protocol[T]):
+    def add(self, x: T, y: T) -> T: ...
+
+
+class IntAdder:
+    def add(self, x: int, y: int) -> int:
+        return x + y
+
+
+class FloatAdder:
+    def add(self, x: float, y: float) -> float:
+        return x + y
+
+
+def add(adder: Adder) -> None:
+    print(adder.add(2, 3))
+
+
+add(IntAdder())
+add(FloatAdder())

python-protocol/adder_v5.py

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+from typing import Protocol
+
+
+class Adder(Protocol):
+    def add[T: int | float | str](self, x: T, y: T) -> T: ...
+
+
+class IntAdder:
+    def add(self, x: int, y: int) -> int:
+        return x + y
+
+
+class FloatAdder:
+    def add(self, x: float, y: float) -> float:
+        return x + y
+
+
+def add(adder: Adder) -> None:
+    print(adder.add(2, 3))
+
+
+add(IntAdder())
+add(FloatAdder())

python-protocol/adder_v6.py

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+from typing import Protocol
+
+
+class Adder(Protocol):
+    def add[T: int | float | str](self, x: T, y: T) -> T: ...
+
+
+class IntAdder:
+    def add(self, x: int, y: int) -> int:
+        return x + y
+
+
+class FloatAdder:
+    def add(self, x: float, y: float) -> float:
+        return x + y
+
+
+class StrAdder:
+    def add(self, x: str, y: str) -> str:
+        return x + y
+
+
+def add(adder: Adder) -> None:
+    print(adder.add(2, 3))
+
+
+add(IntAdder())
+add(FloatAdder())
+add(StrAdder())

python-protocol/animals_v1.py

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+class Animal:
+    def __init__(self, name):
+        self.name = name
+
+    def eat(self):
+        print(f"{self.name} is eating.")
+
+    def drink(self):
+        print(f"{self.name} is drinking.")
+
+
+class Dog(Animal):
+    def bark(self):
+        print(f"{self.name} is barking.")
+
+
+class Cat(Animal):
+    def meow(self):
+        print(f"{self.name} is meowing.")

python-protocol/animals_v2.py

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+class Dog:
+    def __init__(self, name):
+        self.name = name
+
+    def eat(self):
+        print(f"{self.name} is eating.")
+
+    def drink(self):
+        print(f"{self.name} is drinking.")
+
+    def make_sound(self):
+        print(f"{self.name} is barking.")
+
+
+class Cat:
+    def __init__(self, name):
+        self.name = name
+
+    def eat(self):
+        print(f"{self.name} is eating.")
+
+    def drink(self):
+        print(f"{self.name} is drinking.")
+
+    def make_sound(self):
+        print(f"{self.name} is meowing.")

python-protocol/birds_v1.py

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+class Duck:
+    def quack(self):
+        return "The duck is quacking!"
+
+
+def make_it_quack(duck: Duck) -> str:
+    return duck.quack()
+
+
+class Person:
+    def quack(self):
+        return "The person is imitating a duck quacking!"
+
+
+print(make_it_quack(Duck()))
+# print(make_it_quack(Person()))