ophiDIan

Description

ophiDIan is a Dependency Injection (DI) container for Python. Unlike other DI containers that utilize decorators or configuration files to accomplish their goal, ophiDIan uses type hints to identify and resolve dependencies. In other words, by using type hinting to resolve dependencies, ophidIAn avoids making your components dependent upon the DI framework.

Ophidian follows the Register, Resolve, Release (RRR) pattern

Tutorial

Dependency definitions

For this tutorial, we'll use the following class definitions:

from abc import ABC, abstractmethod


class AbstractA(ABC):
    @abstractmethod
    def do_something(self):
        pass


class AbstractB(ABC):
    @abstractmethod
    def do_something_else(self):
        pass


class DependencyA(AbstractA):
    def do_something(self):
        print(f"{id(self)}: I am dependency A")


class DependencyB(AbstractB):
    def __init__(self, name: str):
        self._name = name
    def do_something_else(self):
        print(f"{id(self)} My name is {self._name}")


class TestClass1:
    def __init__(self, a: AbstractA):
        self.a = a


class TestClass2:
    __test__ = False

    def __init__(self, b: AbstractB):
        self.b = b


class TestClass3:
    def __init__(self, a: AbstractA, b: AbstractB):
        self.a = a
        self.b = b

RRR

The first step in the RRR pattern is to Register dependencies. This can be performed using either the register() or register_instance() methods. Next, objects can be built by Resolving. Finally, when the dependency is no longer needed, it can be released.

from ophidian import DIContainer

di_container = DIContainer()
di_container.register(AbstractA, DependencyA)

my_dependency_b = DependencyB("Mike")
di_container.register(AbstractA, DependencyA)
di_container.register_instance(AbstractB, my_dependency_b)

test_class_1 = di_container.resolve(TestClass1)
test_class_2 = di_container.resolve(TestClass2)
test_class_3 = di_container.resolve(TestClass3)

assert id(test_class_1.a) != id(test_class_3.a)
assert id(test_class_2.b) == id(test_class_3.b)
assert isinstance(test_class_1.a, AbstractA)
assert isinstance(test_class_1.a, DependencyA)
assert isinstance(test_class_2.b, AbstractB)
assert isinstance(test_class_2.b, DependencyB)

# Note: All dependencies will automatically be released when the `di_container`
#       instance is cleaned up by the garbage collector.
di_container.release(AbstractA)
di_container.release(AbstractB)

In the above example, the DIContainer.register() method is used tell the DI container that components that depend upon AbstractA should be supplied a new instance of the concrete class DependencyA. The DiContainer.register_instance() method is used to tell the DI container that all components that depend upon AbstractB should be supplied with the same instance of DependencyB.

Conventions

Conventions are mainly used to resolve primitive dependencies. For example, if a component depends upon a file path for a configuration file passed as a string, a convention can be registered to provide the dependency.

from ophidian import DIContainer

class Configuration:
    def __init__(self, a: DependencyA, config_file_path: str):
        ...

di_container = DIContainer()
di_container.register(AbstractA, DependencyA)
di_container.register_convention(str, "config_file_path", "/tmp/my_config_file")

configuration = di_container.resolve(Configuration)

di_container.release(AbstractA)
di_container.release_convention(str, "config_file_path")

We wouldn't want to use register() or register_instance(), as we wouldn't want all string dependencies to be resolved with the configuration file path. Instead, the DI container is informed about an established "convention" within the code: components that depend upon the configuration file path expect a string parameter named "config_file_path". See Primitive Dependencies by Mark Seemann for more information about conventions.