Small DI

The smallest dependency injection mechanism possible in python. SmallDI provides you with intuitive and simple interface for doing dependency injections in your project.

Example usage

import random

from smalldi import Injector
from smalldi.annotation import Provide

# Lets create some service
@Injector.singleton
class MeowService:
    _MEOWS = ["Meow", "Meow-meow", "Meowwwwww", "Mrromeowww", "Meeeeoooow"]
    def __init__(self):
        print("Meow-meow! Meowing service is initialized")
    
    def meow(self):
        print(random.choice(self._MEOWS))

# Now lets make purring service.
# But cats do not purr without telling meow!(at least in this test)
# So its time to inject dependency
@Injector.singleton
class PurrService:
    _PURRS = ["Purrrrr", "Purr-purr"]
    
    @Injector.inject
    def __init__(self, meow_service: Provide[MeowService]):
        self.meow_service = meow_service
        print("Purr-purr! Purring service is initialized")

    def purr(self):
        self.meow_service.meow()
        print(random.choice(self._PURRS))

# Now lets put it all together. 
# Ask our services to meow and then purr
@Injector.inject
def main(meow_service: Provide[MeowService], purr_service: Provide[PurrService]):
    meow_service.meow()
    purr_service.purr()

if __name__ == '__main__':
    main()

Library logic

Injector

Injector is a static class(i.e., one that should never be instantiated) which is the main (and currently the only) DI container inside the library. Injector provides two decorators:

• @Injector.singleton creates an instance of a class which may further be injected in functions
• @Injector.inject replaces parameters annotated with type Provide[Singleton] with actual instances of Singleton

Singletons

Singletons are classes having a single instance. In smalldi singletons may not take constructor(__init__) other than annotated with Provide[] type. Only singletons may be decorated with @Injector.singleton. As a consequence, only singleton classes may be injected at the current state of library development.

Provide

Provide[T] is an annotation for injector telling it that instead of this argument instance of T should be passed. Caller of function with Provide[T] may explicitly override argument annotated with Provide[T] by directly passing annotated_di_arg=my_value.