pydres 0.1.1

A simple dependency resolver

pydres: Python Dependency Resolver

pydres (Python Dependency Resolver) is a lightweight and flexible library to instantiate Python classes with resolved dependencies. It supports hierarchical, string-based, and custom class annotations for dependency injection. With pydres, you can easily manage and override dependencies for your Python classes, even when dealing with complex dependency chains.

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Features

• Resolves both class and string-based type annotations.
• Enables dependency overriding by parameter name or type.
• Recursively instantiates classes based on their constructors.
• Provides utility functions for inspecting and resolving dependencies.

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Installation

Install pydres via pip:

pip install pydres

Or via Poetry:

poetry add pydres

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Usage

Basic Dependency Resolution

from pydres import instantiate_with_dependencies

class B:
    def __init__(self, message: str = "default message"):
        self.message = message

class A:
    def __init__(self, b: B):
        self.b = b

# Automatically resolves and instantiates dependencies
instance = instantiate_with_dependencies(A)
print(instance.b.message)  # Output: default message

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Overriding Dependencies

overrides = {
    "message": "custom message"
}

instance = instantiate_with_dependencies(B, overrides)
print(instance.message)  # Output: custom message

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Resolving String-Based Annotations

class C:
    pass

class B:
    def __init__(self, c: "C"):
        self.c = c

instance = instantiate_with_dependencies(B)
print(isinstance(instance.c, C))  # Output: True

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Handling Circular Dependencies

pydres handles most dependency chains but will raise an error for unresolved circular dependencies.

class J:
    def __init__(self, k: "K"):
        self.k = k

class K:
    def __init__(self, j: J):
        self.j = j

# This will raise a RecursionError
instantiate_with_dependencies(J)

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Resolving Multiple Levels of Dependencies

class Inner:
    def __init__(self, x: int):
        self.x = x

class Outer:
    def __init__(self, inner: Inner):
        self.inner = inner

overrides = {"x": 42}
instance = instantiate_with_dependencies(Outer, overrides)
print(instance.inner.x)  # Output: 42

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Utilities

pydres also includes helper methods to inspect and manipulate dependency structures.

• get_first_custom_init(cls: Type[Any]) -> Optional[Callable[..., None]]: Get the first custom __init__ in the inheritance chain.
• is_builtin_type(param_type: Any) -> bool: Check if a type is a built-in Python type.
• is_custom_class(param_type: Any) -> bool: Check if a type is a user-defined class.
• resolve_dependency(...): Resolve a single dependency using overrides or recursive instantiation.

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Testing

pydres includes comprehensive tests with pytest.

To run the tests locally:

pytest --cov=pydres --cov-report=html

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Contributing

Contributions are welcome! To contribute:

1. Fork the repository.
2. Create a feature branch.
3. Submit a pull request.

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License

This project is licensed under the MIT License. See the LICENSE file for details.

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Acknowledgments

Special thanks to the open-source community for providing the inspiration and tools necessary to build this project.