Introduction to mypy-protobuf

mypy-protobuf is a powerful tool that enables static type checking for Protocol Buffers within Python. It integrates seamlessly with mypy, the static type checker for Python, enhancing type safety and helping catch potential bugs early in the development cycle.

API Examples and Usage

Here, we explore various APIs provided by mypy-protobuf and illustrate with code snippets.

Setting Up mypy-protobuf

  pip install mypy-protobuf

After installation, you can convert your .proto files into Python files with type annotations.

Generating Python Code from .proto Files

  protoc --python_out=. --mypy_out=. example.proto

This command generates Python code with type annotations from your Protocol Buffer definitions.

Defining a .proto File

  syntax = "proto3";
  package example;

  message User {
    string name = 1;
    int32 id = 2;
    string email = 3;
  }

Working with Generated Code

Once you’ve generated the Python code, you can use it with MyPy to check types:

  from example_pb2 import User

  def get_user() -> User:
      return User(name="John", id=123, email="john@example.com")

Using mypy for Type Checking

  def greet_user(user: User) -> str:
      return f"Hello, {user.name}!"

  user = get_user()
  print(greet_user(user))

Run mypy to ensure type safety:

  mypy script.py

Example Application Using mypy-protobuf

Below is an example of a simple application that demonstrates the power of type checking with mypy-protobuf.

example.proto

  syntax = "proto3";
  package example;

  message Product {
    string name = 1;
    int32 id = 2;
  }

  message Order {
    int32 order_id = 1;
    repeated Product products = 2;
  }

Application Code

  from example_pb2 import Product, Order

  def create_order(order_id: int, products: list[Product]) -> Order:
      return Order(order_id=order_id, products=products)
  
  def main() -> None:
      product1 = Product(name="Product1", id=1)
      product2 = Product(name="Product2", id=2)
      order = create_order(101, [product1, product2])
      print(f"Order ID: {order.order_id}, Products: {[p.name for p in order.products]}")

  if __name__ == "__main__":
      main()

Ensure type safety by running mypy:

  mypy app.py

This example showcases the benefits of type-checking in improving code reliability and reducing runtime errors with the help of mypy-protobuf.

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