Dicon, simple DI container injection liblary for Python.

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Dicon is a simple "DI container injection" library.

FAQ

• Q. Is dicon a dependency injection library?
• A. No, it does not support dependency injection. It supports DI container injection and service (singleton) locator.

Important points

• Simple to use.
• Clear what it does on each stage.
• Small overhead.

Features

• @dicon.inject_di_container class decorator supports nested DI container injection, without modification on type.
• dicon.DIContainer provides class resolver and singleton locating.

Class resolver, no modification on type

import dicon

class A:
    pass
    
di_container = dicon.DIContainer()
di_container.register[A]()
di_container.freeze()

# Resolve class.
class_A = di_container.resolve[A]
a = class_A()
# dicon.DIContainer does not modify type of the object.
assert type(a) is A
# It only modifies constructor.  (Normally it will be not a problem.)
assert not (class_A is A)

Nested DI container injection

@dicon.inject_di_container('_di_container')
class B:
    _di_container = None # Here we get instance of DIContainer.

    def __init__(self, message):
        print(message, self._di_container)

@dicon.inject_di_container('_di_container')
class C:
    _di_container = None # Here we get instance of DIContainer.

    def __init__(self):
        self._b = self._di_container.resolve[B]('B must be have DIContainer:')

di_container = dicon.DIContainer()
di_container.register[B]()
di_container.register[C]()
di_container.freeze()

di_container.resolve[C]()
# will print 'B must be have DIContainer: ...'

Singleton locating

TBW...

How it works

1. @dicon.inject_di_container modifies __init__ of given class to make it possible __init__ can take DIContainer as an argument.
2. DIContainer.resolve ties itself to that argument by functools.partial.

That's all.

For more details, see tests.

Other existing solutions

• Dependency injection
  • There are lots of DI libraries: for example, injector, pinject.
    • IMHO, DI is too complex for python.
    • Famous liblaries are too complex and not clear how affect to the program.
    • It seems no one support nested injection.
• Service locator
  • wired
    • I personally felt it is too complex.
  • factoryfactory
    • It does not support multiple service locators.

I borrowed design of MicroResolver in API.