Python Injection Framework (PIF)

A simple Python dependency injection framework.

Usage

This project is under active development. The following example does not represent the final state for the project.

You can install this project from pypi.

pip install python-injection-framework

Dependency Injection

The injection framework is configured to inject any default values for method arguments that are instances of providers.Provider.

This implementation works by wrapping decorators around methods any patching any unfilled providers.Provider default arguments at runtime.

All dependency injection is lazily evaluated so providers are only evaluated when a method is called. This approach is optimal as it reduces necessary computation for expensive services and reduces

Decorator Injection

With this approach you can automatically inject functions at load time using the @wiring.inject decorator.

from pif import wiring, providers


@wiring.inject  # <- automatically injects providers.Provider default arguments!
def my_function(a: str = providers.ExistingSingleton("hello world")):
    return a


if __name__ == "__main__":
    assert "hello world" == my_function()

Module Injection

With this approach you can wire all methods in the specified modules.

from pif import wiring, providers


def my_function(a: str = providers.ExistingSingleton("hello world")):
    return a


if __name__ == "__main__":
    wiring.wire([__name__])  # <- dynamically inject methods with providers.Provider default arguments!

    assert "hello world" == my_function()

Overriding

This package provides a simple mechanism to override providers. This can be very useful when it comes to mocking services for testing or dynamically patching application behavior based on application configuration.

Standard Overriding

If you want to patch a value all you need to do is call .override() on the provider in question. If you are wanting to override an existing singleton you may call the convenience method .override_existing().

from pif import wiring, providers

StringProvider = providers.ExistingSingleton("hello world")


@wiring.inject
def my_function(a: str = StringProvider):
    return a


if __name__ == "__main__":
    assert "hello world" == my_function()

    override = StringProvider.override_existing("overridden_1")

    assert "overridden_1"

Context Managers

If you want more control around the override lifecycles then you may use the Override context manager.

from pif import wiring, providers

StringProvider = providers.ExistingSingleton("hello world")


@wiring.inject
def my_function(a: str = StringProvider):
    return a


if __name__ == "__main__":
    assert "hello world" == my_function()

    OverrideProvider = providers.ExistingSingleton("overridden_1")

    with StringProvider.override(OverrideProvider):
        assert "overridden_1" == my_function()

        with OverrideProvider.override_existing("overridden_2"):
            assert "overridden_2" == my_function()  # You can even stack overrides!!

        assert "overridden_1" == my_function()

    assert "hello world" == my_function()

Examples

If you would like to see more examples, feel free to check out examples/.

Contributing

1. Clone the repository and configure Poetry 🪄

   git clone git@github.com:scottzach1/Python-Injection-Framework.git
   cd Python-Injection-Framework
   poetry install

2. Configure pre-commit hooks 🪝

   pre-commit install

3. Write your changes! 💻️

4. Run test cases 🧪

   pytest tests/

5. Submit a Pull Request ↖️

Authors

Zac Scott (scottzach1)