Injection on a decorator

[platipo]

Hi, I really like this package and am using it in production. I was tying to mess around with decorators because I want to add side effects to a function, adding a secret_number in the example. I was expecting decorated_function_1 to work but it didn't and I can't wrap my head around it. Is this an expected behavior? Could injection be supported like in my_decorator_1?

I also added few examples of things I tried and only decorated_function_4 actually works.

from functools import wraps

from dependency_injector import containers, providers
from dependency_injector.wiring import Provide, inject


class Container(containers.DeclarativeContainer):
    config = providers.Configuration()


@inject
def my_decorator_1(func, secret_number: int = Provide[Container.config.secret_number]):
    @wraps(func)
    def wrapper(*args, **kwargs):
        result = func(*args, **kwargs)
        return result + secret_number
    return wrapper

@inject
def my_decorator_2(secret_number: int = Provide[Container.config.secret_number]):
    def inner_decorator(func):
        @wraps(func)
        def wrapper(*args, **kwargs):
            result = func(*args, **kwargs)
            return result + secret_number
        return wrapper
    return inner_decorator

def my_decorator_3():
    @inject
    def inner_decorator(func, secret_number: int = Provide[Container.config.secret_number]):
        @wraps(func)
        def wrapper(*args, **kwargs):
            result = func(*args, **kwargs)
            return result + secret_number
        return wrapper
    return inner_decorator

def my_decorator_4(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        result = func(*args, **kwargs)
        secret_number = kwargs['secret_number']
        return result + secret_number
    return wrapper


@my_decorator_1
def decorated_function_1():
    return 42

@inject
@my_decorator_1
def decorated_function_1a():
    return 42

@my_decorator_2()
def decorated_function_2():
    return 42

@my_decorator_3()
def decorated_function_3():
    return 42

@inject
@my_decorator_3()
def decorated_function_3a():
    return 42

@inject
@my_decorator_4
def decorated_function_4(secret_number: int = Provide[Container.config.secret_number]):
    return 42

@my_decorator_4
@inject
def decorated_function_4a(secret_number: int = Provide[Container.config.secret_number]):
    return 42


def main():
    test_funcs = [
        decorated_function_1,
        decorated_function_1a,
        decorated_function_2, 
        decorated_function_3, 
        decorated_function_3a,
        decorated_function_4, 
        decorated_function_4a, 
    ]
    for test_f in test_funcs:
        try:
            result = test_f()
            print(f"Function {test_f} returned {result}")
        except Exception as exc:
            print(f"Function {test_f} raised {exc.__class__.__name__} '{exc}'")

if __name__ == '__main__':
    import sys

    container = Container()
    container.init_resources()
    container.config.secret_number.from_env("SECRET_INT", 24)
    container.wire(modules=[sys.modules[__name__]])

    main()

The output is:

Function <function decorated_function_1 at 0x7f93d8a4d310> raised TypeError 'unsupported operand type(s) for +: 'int' and 'Provide''
Function <function decorated_function_1a at 0x7f93d8a4d4c0> raised TypeError 'unsupported operand type(s) for +: 'int' and 'Provide''
Function <function decorated_function_2 at 0x7f93d8a4d670> raised TypeError 'unsupported operand type(s) for +: 'int' and 'Provide''
Function <function decorated_function_3 at 0x7f93d8a4d820> raised TypeError 'unsupported operand type(s) for +: 'int' and 'Provide''
Function <function decorated_function_3a at 0x7f93d8a4daf0> raised TypeError 'unsupported operand type(s) for +: 'int' and 'Provide''
Function <function decorated_function_4 at 0x7f93d8a4dca0> returned 66
Function <function decorated_function_4a at 0x7f93d8a4de50> raised KeyError ''secret_number''

[MatthieuMoreau0]

Hi, I noticed the same issue on my project. The container doesn't inject properly in the arguments of my decorator function.

Thanks for your experimentations, I'll use the workaround presented in your my_decorator_4 for now.

Are there any plans to fix this issue ? I'm wondering why this even occurs specifically on decorator among all functions..

[rmk135]

Hey @platipo and @MatthieuMoreau0 ,

Found a solution after some debugging:

def my_decorator_1(func):
    @wraps(func)
    @inject
    def wrapper(
            *args,
            secret_number: int = Provide[Container.config.secret_number],
            **kwargs,
    ):
        result = func(*args, **kwargs)
        return result + secret_number
    return wrapper


def my_decorator_2():
    def inner_decorator(func):
        @wraps(func)
        @inject
        def wrapper(
                *args,
                secret_number: int = Provide[Container.config.secret_number],
                **kwargs,
        ):
            result = func(*args, **kwargs)
            return result + secret_number
        return wrapper
    return inner_decorator


def my_decorator_3():
    def inner_decorator(func, ):
        @wraps(func)
        @inject
        def wrapper(
                *args,
                secret_number: int = Provide[Container.config.secret_number],
                **kwargs,
        ):
            result = func(*args, **kwargs)
            return result + secret_number
        return wrapper
    return inner_decorator


def my_decorator_4(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        result = func(*args, **kwargs)
        secret_number = kwargs['secret_number']
        return result + secret_number
    return wrapper

This way it produces expected output for all functions (except decorated_function_4a that seems to be not working anyway):

(venv) ➜  issue454 git:(develop) ✗ python example.py
Function <function decorated_function_1 at 0x106518d30> returned 66
Function <function decorated_function_1a at 0x106518f70> returned 66
Function <function decorated_function_2 at 0x10651e1f0> returned 66
Function <function decorated_function_3 at 0x10651e430> returned 66
Function <function decorated_function_3a at 0x10651e040> returned 66
Function <function decorated_function_4 at 0x10651e790> returned 66
Function <function decorated_function_4a at 0x10651e940> raised KeyError ''secret_number''

To make injections work with decorators you need to inject dependencies into a decorating closure, but not a decorator itself. Otherwise the actual call of the decorator happens before the config value is defined.

PS: My apologies it took that long to answer.

[rmk135]

Closing this issue for now. Please re-open or comment if needed.

[fabiocerqueira]

from functools import wraps

from dependency_injector import containers, providers
from dependency_injector.wiring import Provide, inject


class Reporter:
    def info(self, msg):
        print(f"*** [INFO] {msg}")


class Container(containers.DeclarativeContainer):
    conf = providers.Configuration()
    reporter = providers.Singleton(Reporter)


def tagger(tag):
    def inner(func):
        # @wraps(func)  # <-- using wraps break inject
        @inject
        def tagger_wrapper(text, sep=Provide[Container.conf.sep], **kwargs):
            result = func(text, **kwargs)
            return f"{result}{sep}({tag}[{func.__name__}])"

        return tagger_wrapper

    return inner


def logger(prefix):
    def inner(func):
        # @wraps(func)  # <-- using wraps break inject
        @inject
        def logger_wrapper(text, reporter=Provide[Container.reporter], **kwargs):
            result = func(text, **kwargs)
            reporter.info(f"{prefix} - {func.__name__}('{text}') was called")
            return result

        return logger_wrapper

    return inner


def helper(tag, prefix):
    def inner(func):
        @tagger(tag)
        @wraps(func)  # <-- if remove this double wraps it breaks the function name
        @logger(prefix)
        @inject
        @wraps(func)
        def helper_wrapper(text, **kwargs):
            result = func(text, **kwargs)
            return result

        return helper_wrapper

    return inner


@helper("my_tag", "|my_prefix|")
def my_example(text):
    return text


if __name__ == "__main__":
    container = Container()
    container.wire(modules=[__name__])
    container.conf.from_dict({"sep": " / "})
    print(my_example("hi!"))

Running the example above we get the expected behaviour

*** [INFO] |my_prefix| - my_example('hi!') was called
hi! / (my_tag[my_example])

If you try to remove this double @wraps call in helper the function name breaks:

*** [INFO] |my_prefix| - my_example('hi!') was called
hi! / (my_tag[logger_wrapper])
              ^^^^^^^^^^^^^^^^

if I move the @wraps to the decorator(this I think should be the correct way) it breaks @inject

Traceback (most recent call last):
  File "example.py", line 69, in <module>
    print(my_example("hi!"))
  File "/home/fabio/.pyenv/versions/.../dependency_injector/wiring.py", line 612, in _patched
    result = fn(*args, **to_inject)
  File "example.py", line 22, in tagger_wrapper
    result = func(text, **kwargs)
  File "/home/fabio/.pyenv/versions/.../dependency_injector/wiring.py", line 612, in _patched
    result = fn(*args, **to_inject)
  File "example.py", line 36, in logger_wrapper
    reporter.info(f"{prefix} - {func.__name__}('{text}') was called")
AttributeError: 'Provide' object has no attribute 'info'

[Jitesh-Khuttan]

@fabiocerqueira I faced the same issue as well, adding wraps is breaking the inject.

@rmk135 could you please have a look?

My use case is similar to what Fabio mentioned:

def tagger(tag):
    def inner(func):
        # @wraps(func)  # <-- using wraps break inject
        @inject
        def tagger_wrapper(text, sep=Provide[Container.conf.sep], **kwargs):
            result = func(text, **kwargs)
            return f"{result}{sep}({tag}[{func.__name__}])"

        return tagger_wrapper

    return inner

[rmk135]

Hey @Jitesh-Khuttan @fabiocerqueira ,

First, thanks a lot for finding the issue and providing steps to reproduce it. It's uneasy to catch. After 3 rounds of debugging, I've localized the root cause. The problem is that the second @wraps(func) where func is already @inject-patched function, overrides previously parsed injections.

There is no easy fix, but I have one refactoring in mind that theoretically could help. I'll proceed with it and get back when I have any news.

[rmk135]

Linking this with #597