What is a Protocol in python?

In Python, protocols refer to a concept introduced in Python 3.8 as a way to define structural typing or "duck typing" within the language. A protocol is a set of methods or attributes that an object must have in order to be considered compatible with that protocol. Protocols enable you to define interfaces without explicitly creating a class or inheriting from a specific base class.

Protocols are defined using the typing.Protocol class or the typing.Protocol decorator. Let's explore the details with examples:

Defining a Protocol:
To define a protocol, you can use the typing.Protocol class or the typing.Protocol decorator. Here's an example using the class syntax:

from typing import Protocol

class Printable(Protocol):
    def print(self) -> None:
        pass

In this example, we define a protocol named Printable that requires an object to have a print method. The Protocol class allows you to define abstract methods (in this case, just print) that must be implemented by objects conforming to the protocol.

Implementing a Protocol:
To implement a protocol, you don't need to explicitly declare it. Instead, you can ensure that an object conforms to a protocol by implementing the required methods. Here's an example:

class Book:
    def __init__(self, title: str):
        self.title = title

    def print(self) -> None:
        print(f"Book Title: {self.title}")

In this example, the Book class implements the Printable protocol by providing the required print method. Any instance of the Book class can be treated as a Printable object.

Using a Protocol:
Protocols are primarily used for type hinting and static type checking. You can use a protocol as a type annotation to indicate that an argument or variable must conform to a specific protocol. Here's an example:

def print_object(obj: Printable) -> None:
    obj.print()

In this example, the print_object function takes an argument obj of type Printable. This means that any object passed to this function must implement the print method defined in the Printable protocol.

Multiple Protocols:
You can also define a protocol that combines multiple other protocols. Here's an example:

class Serializable(Protocol):
    def serialize(self) -> str:
        pass

class PrintableAndSerializable(Printable, Serializable):
    pass

In this example, we define a protocol named Serializable with a serialize method. Then we define another protocol named PrintableAndSerializable that combines both the Printable and Serializable protocols.

To conclude with,Protocols provide a way to define structural typing in Python, allowing you to create interfaces without the need for explicit inheritance. They enable type checkers to verify that objects adhere to the defined protocols, enhancing code correctness and maintainability.