Opyoid

Dependency injection library using typings, to easily manage large applications.

This project is inspired from Guice.

Installation

Run pip install opyoid to install from PyPI.

Run pip install . to install from sources.

This project follows the Semantic Versioning Specification. All breaking changes are described in the Changelog.

Usage

Simple Injection

from opyoid import Module, Injector


class MyClass:
    pass


class MyParentClass:
    def __init__(self, my_param: MyClass):
        self.my_param = my_param


class MyModule(Module):
    def configure(self) -> None:
        self.bind(MyClass)
        self.bind(MyParentClass)


injector = Injector([MyModule])
my_instance = injector.inject(MyParentClass)
assert isinstance(my_instance, MyParentClass)
assert isinstance(my_instance.my_param, MyClass)

If they are multiple bindings for the same class, the latest will be used.

Module

The module is used to group bindings related to a feature. You can include a module in another with install:

from opyoid import Module, Injector


class MyClass:
    pass


class MyModule(Module):
    def configure(self) -> None:
        self.bind(MyClass)


class MyParentClass:
    def __init__(self, my_param: MyClass):
        self.my_param = my_param


class MyParentModule(Module):
    def configure(self) -> None:
        self.install(MyModule)
        self.bind(MyParentClass)


injector = Injector([MyParentModule])
my_instance = injector.inject(MyParentClass)
assert isinstance(my_instance, MyParentClass)
assert isinstance(my_instance.my_param, MyClass)

Binding Subclasses

from opyoid import Module, Injector


class MyClass:
    pass


class MySubClass(MyClass):
    pass


class MyModule(Module):
    def configure(self) -> None:
        self.bind(MyClass, to_class=MySubClass)

injector = Injector([MyModule])
my_instance = injector.inject(MyClass)
assert isinstance(my_instance, MySubClass)

Binding Instances

from opyoid import Module, Injector


class MyClass:
    def __init__(self, my_param: str):
        self.my_param = my_param

my_instance = MyClass("hello")


class MyModule(Module):
    def configure(self) -> None:
        self.bind(MyClass, to_instance=my_instance)


injector = Injector([MyModule])
injected_instance = injector.inject(MyClass)
assert my_instance is injected_instance

Environment Variables

You can use environment variables to easily override bindings in your application.

Supported types

Supported types are str, int, float, and bool.

Environment variables are only used when loading ClassBindings, ProviderBindings or SelfBindings, not InstanceBindings

If the corresponding environment variable exists, it will override the existing default value and bindings for the parameter.

Environment variable name

The environment variable should be named UPPER_CLASS_NAME_UPPER_PARAMETER_NAME In this example, the environment variable to set is MY_CLASS_MY_PARAMETER:

@dataclass
class MyClass:
    my_parameter: int

Value conversion

For types other than str, an automatic conversion is made:

• ints and floats are converted using int() and float()
• for booleans, authorized values are:
  • "0", "false" and "False", will be converted to False
  • "1", "true" and "True", will be converted to True

Binding scopes

When binding a class, you can choose the scope in which it will be instantiated. This will only have an effect when binding classes, not instances.

Singleton Scope

By default, all classes are instantiated in a Singleton scope. This means that only one instance of each class will be created, and it will be shared between all classes requiring it.

from opyoid import Module, Injector, SingletonScope


class MyClass:
    pass


class MyParentClass:
    def __init__(self, my_param: MyClass):
        self.my_param = my_param


class MyModule(Module):
    def configure(self) -> None:
        self.bind(MyClass, scope=SingletonScope)
        self.bind(MyParentClass, scope=SingletonScope)

injector = Injector([MyModule])
instance_1 = injector.inject(MyClass)
instance_2 = injector.inject(MyClass)
parent_instance = injector.inject(MyParentClass)
assert instance_1 is instance_2
assert instance_1 is parent_instance.my_param

PerLookup Scope

If you use the per lookup scope, a new instance will be created every time each class is injected.

from opyoid import Module, Injector, PerLookupScope


class MyClass:
    pass


class MyParentClass:
    def __init__(self, my_param: MyClass):
        self.my_param = my_param


class MyModule(Module):
    def configure(self) -> None:
        self.bind(MyClass, scope=PerLookupScope)
        self.bind(MyParentClass)

injector = Injector([MyModule])
instance_1 = injector.inject(MyClass)
instance_2 = injector.inject(MyClass)
parent_instance = injector.inject(MyParentClass)
assert instance_1 is not instance_2
assert instance_1 is not parent_instance.my_param

Thread Scope

This scope only creates a new instance the first time that the class is injected in the current thread. There will only be one instance of each class in each thread, and two instances injected from different threads will be different objects.

from threading import Thread

from opyoid import Module, Injector, ThreadScope


class MyClass:
    pass


class MyModule(Module):
    def configure(self) -> None:
        self.bind(MyClass, scope=ThreadScope)

injector = Injector([MyModule])
instance_1 = injector.inject(MyClass)
instance_2 = injector.inject(MyClass)

def thread_target():
    instance_3 = injector.inject(MyClass)
    assert instance_1 is not instance_3

Thread(target=thread_target).start()

assert instance_1 is instance_2

Bindings without Module

If you prefer, you can add bindings to your injector without creating a Module class (or using both).

from opyoid import Module, Injector, SelfBinding


class MyClass:
    pass


class MyParentClass:
    def __init__(self, my_param: MyClass):
        self.my_param = my_param


class MyModule(Module):
    def configure(self) -> None:
        self.bind(MyClass)


injector = Injector([MyModule], [SelfBinding(MyParentClass)])
my_instance = injector.inject(MyParentClass)
assert isinstance(my_instance, MyParentClass)
assert isinstance(my_instance.my_param, MyClass)

The same options of Module.bind are available when using bindings:

from opyoid import ClassBinding, InstanceBinding, PerLookupScope, SelfBinding


class MyClass:
    pass


class MySubClass(MyClass):
    pass

my_instance = MyClass()

SelfBinding(MyClass)  # binding a class to itself
ClassBinding(MyClass, MySubClass)  # binding a class to a subclass
SelfBinding(MyClass, scope=PerLookupScope)  # specifying scope
InstanceBinding(MyClass, my_instance)  # binding an instance
SelfBinding(MyClass, named="my_name")  # binding a class to itself with a specific name
InstanceBinding(MyClass, my_instance, named="my_name")  # binding an instance with a specific name

Injecting Type

If no explicit binding is defined, the last class binding will be used to inject a type:

from typing import Type

from opyoid import Module, Injector

class MyClass:
    pass

class SubClass(MyClass):
    pass

class MyParentClass:
    def __init__(self, my_param: Type[MyClass]):
        self.my_param = my_param

my_instance = MyClass()

class MyModule(Module):
    def configure(self) -> None:
        self.bind(MyClass)
        self.bind(MyClass, to_instance=my_instance)
        self.bind(MyClass, to_class=SubClass)
        self.bind(MyParentClass)


injector = Injector([MyModule])
parent_instance = injector.inject(MyParentClass)
assert isinstance(parent_instance, MyParentClass)
assert parent_instance.my_param is SubClass

Dataclasses

opyoid can inject classes and parameters defined with the attrs library and python data classes.

Notes about Generics

• The supported generic types are List, Set, Tuple, Optional, Union and Type (and any combination of them). Other generics must be bound explicitly (e.g. you must bind a dict to Dict[str, MyClass] if you want to inject it).
• Be careful when using generics, the bindings will only be used if the type matches exactly. For example, you cannot implicitly bind MyClass[T] to inject MyClass, or MyClass[str] to inject MyClass[T]. You need to bind something to MyClass[str] to be able to inject it.

Advanced usage

More advanced features and examples are available in the ./docs folder.