Incorrect Example In The Docs About `WithParents`

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Understanding the Issue

The provided example in the documentation for WithParents in the dishka library contains an incorrect instantiation of the Protocol class. This issue can lead to confusion and incorrect usage of the WithParents feature. In this article, we will delve into the details of the problem, explore the correct usage of Protocol, and provide a revised example that demonstrates the proper usage of WithParents.

What is Protocol?

Protocol is a type from the typing module in Python that represents a protocol, which is essentially an abstract base class that defines a set of methods that must be implemented by any class that conforms to the protocol. Protocols are useful for defining interfaces or abstract classes that can be used to specify the behavior of a class without requiring the class to inherit from a specific base class.

Instantiating Protocol

As shown in the example, attempting to instantiate Protocol directly will raise a TypeError. This is because protocols are abstract and cannot be instantiated directly. Instead, you must create a class that conforms to the protocol by implementing the required methods.

Correcting the Example

To correct the example, we need to create a class that conforms to the A protocol. Here's an updated example:

from dishka import WithParents, provide, Provider, Scope
from typing import Protocol

class A(Protocol):
    def method(self) -> None:
        ...

class AImpl(A):
    def method(self) -> None:
        print("Implementing method")

class MyProvider(Provider):
    scope = Scope.APP

    @provide
    def a(self) -> WithParents[AImpl]:
        return AImpl()

container = make_async_container(MyProvider())
a = await container.get(A)
a = await container.get(AImpl)
a is a  # True

In this corrected example, we define a class AImpl that conforms to the A protocol by implementing the method method. We then create an instance of AImpl and return it from the MyProvider class.

Using WithParents Correctly

WithParents is a feature in the dishka library that allows you to specify a set of parent classes that a provider must implement. To use WithParents correctly, you must create a class that conforms to the specified protocol and return an instance of that class from the provider.

Here's an updated example that demonstrates the correct usage of WithParents:

from dishka import WithParents, provide, Provider, Scope
from typing import Protocol

class A(Protocol):
    def method(self) -> None:
        ...

class AImpl(A):
    def method(self) -> None:
        print("Implementing method")

class B(Protocol):
    def method(self) -> None:
        ...

class BImpl(B):
    def method(self) -> None:
        print("Implementing method")

class MyProvider(Provider):
    scope = Scope.APP

    @provide
    def a(self) -> WithParents[AImpl, BImpl]:
        return AImpl()

container = make_async_container(MyProvider())
a = await container.get(A)
b = container.get(B)
a is a  # True
b is b  # True

In this example, we define two protocols A and B and create classes AImpl and BImpl that conform to those protocols. We then create a provider MyProvider that returns an instance of AImpl from the a method. We also specify that the provider must implement both A and B protocols using the WithParents feature.

Conclusion

In conclusion, the provided example in the documentation for WithParents in the dishka library contains an incorrect instantiation of the Protocol class. To correct this issue, we must create a class that conforms to the specified protocol and return an instance of that class from the provider. By following the correct usage of WithParents, we can ensure that our providers are correctly implemented and our applications function as expected.

Best Practices

To avoid similar issues in the future, here are some best practices to keep in mind:

  • Always create a class that conforms to the specified protocol before attempting to instantiate it.
  • Use the WithParents feature to specify the set of parent classes that a provider must implement.
  • Ensure that your providers return instances of classes that conform to the specified protocols.
  • Test your providers thoroughly to ensure that they are correctly implemented and functioning as expected.

Frequently Asked Questions

In this article, we will address some of the most frequently asked questions about WithParents in dishka. Whether you're a seasoned developer or just starting out, this Q&A will help you understand the ins and outs of WithParents and how to use it effectively in your applications.

Q: What is WithParents in dishka?

A: WithParents is a feature in the dishka library that allows you to specify a set of parent classes that a provider must implement. It's a powerful tool for creating robust and maintainable applications.

Q: How do I use WithParents in my provider?

A: To use WithParents in your provider, you need to specify the set of parent classes that the provider must implement. You can do this by using the WithParents decorator and passing in the parent classes as arguments.

from dishka import WithParents, provide, Provider, Scope

class A(Protocol):
    def method(self) -> None:
        ...

class AImpl(A):
    def method(self) -> None:
        print("Implementing method")

class MyProvider(Provider):
    scope = Scope.APP

    @provide
    def a(self) -> WithParents[AImpl]:
        return AImpl()

Q: What are the benefits of using WithParents?

A: Using WithParents provides several benefits, including:

  • Improved code organization: By specifying the set of parent classes that a provider must implement, you can keep your code organized and easy to maintain.
  • Increased robustness: WithParents helps ensure that your providers are correctly implemented and functioning as expected.
  • Better scalability: By using WithParents, you can create applications that are more scalable and maintainable.

Q: How do I test my providers with WithParents?

A: Testing your providers with WithParents is similar to testing any other provider. You can use the dishka testing framework to create test cases and verify that your providers are correctly implemented.

import pytest
from dishka import make_async_container

@pytest.fixture
def container():
    return make_async_container(MyProvider())

def test_a(container):
    a = container.get(A)
    assert a.method() is None

Q: What are some common pitfalls to avoid when using WithParents?

A: Here are some common pitfalls to avoid when using WithParents:

  • Incorrectly specifying parent classes: Make sure to specify the correct parent classes when using WithParents.
  • Failing to implement required methods: Ensure that you implement all required methods in your provider.
  • Not testing your providers thoroughly: Test your providers thoroughly to ensure that they are correctly implemented and functioning as expected.

Q: How do I troubleshoot issues with WithParents?

A: If you encounter issues with WithParents, here are some steps you can take to troubleshoot the problem:

  • Check your code: Review your code to ensure that you are usingWithParents` correctly.
  • Verify your dependencies: Make sure that your dependencies are correctly installed and configured.
  • Consult the documentation: Refer to the dishka documentation for more information on using WithParents.

By following these best practices and troubleshooting tips, you can ensure that your applications are robust, maintainable, and scalable.