Use mixins with AbstractProvider path to race conditioning for youre provider

[therb1]

When super().__init__() is executed, the __init__ function in all mixins is executed.
Just because there is no __init__ function in AbstractProvider, the __init__ function of all subsequent mixins is not executed.

To work around the problem, you need to put AbstractProvider at the end of the list, after all mixins.

Do you plan to do something about this?
You can add __init__ to AbstractProvider, but I'm not sure if this is the right solution.

Here is an example of how I got this problem

from openfeature.provider.provider import AbstractProvider
from openfeature import api
from src.python_sdk_provider.mixins import ClientMixin
from src.python_sdk_provider.mixins import ParameterEventsMixin
from src.python_sdk_provider.mixins import FlagResolutionMixin
from src.python_sdk_provider.mixins import UpdateMixin
from src.python_sdk_provider.mixins import LogsMixin
from src.python_sdk_provider.mixins import MetricsMixin

class Provider(
    ClientMixin,
    ParameterEventsMixin,
    FlagResolutionMixin,
    UpdateMixin,
    AbstractProvider, <-- here's a problem
    MetricsMixin, <-- Dont execute def __init__
    LogsMixin, <-- Dont execute def __init__
):
    def __init__(self):
        super().__init__()
        self.openfeature_backend_url = ""
_...more code..._

[beeme1mr]

Hey @therb1, I'm not sure I fully understand the issue. Would it be possible to provide a minimal recreation of the problem? Including @federicobond @gruebel for visibility.

[gruebel]

I can give some insights. This is an MRO (Method Resolution Order) issue with typing.Protocol. Protocol is not a normal class and therefore the call chain breaks there.

I could add a bandaid, but I'm not sure, if this is something we actually want to do. The other possibility is to keep it as is and @therb1 would need to invoke the __init__() function for each of his Mixin classes, ex.

class Provider(
    ClientMixin,
    AbstractProvider,
    LogsMixin,
):
    def __init__(self):
        ClientMixin.__init__(self)
        LogsMixin.__init__(self)

or as he mentioned put AbstractProvider at the end of the MRO.

[therb1]

Hey @therb1, I'm not sure I fully understand the issue. Would it be possible to provide a minimal recreation of the problem? Including @federicobond @gruebel for visibility.

If I put the provider at the end, the code works as expected

from openfeature.provider.provider import AbstractProvider
import asyncio


class MetricsMixin:
    def __init__(self):
        super().__init__()
        self._using_custom_registry = "registry"

    def start_metrics_server(self):
        if not self._using_custom_registry:
            print("without problem")


class Provider(MetricsMixin, AbstractProvider):
    def __init__(
        self,
    ):
        super().__init__()

    def get_metadata(self):
        pass

    def resolve_boolean_details(self):
        pass

    def resolve_string_details(self):
        pass

    def resolve_integer_details(self):
        pass

    def resolve_object_details(self):
        pass

    def resolve_float_details(self):
        pass

    async def initialize(self):
        print("Provider initialized.")

        self.start_metrics_server()

        print("Provider shutdown.")


async def main():
    provider = Provider()
    await provider.initialize()


if __name__ == "__main__":
    asyncio.run(main())

Output:

developer@Mhs1kq:/workspaces/python-sdk-provider$ poetry run python -u "/workspaces/python-sdk-provider/test.py"
Provider initialized.
Provider shutdown.

But if I put AbstractProvider first in the queue, I get an initialization failure

from openfeature.provider.provider import AbstractProvider
import asyncio


class MetricsMixin:
    def __init__(self):
        super().__init__()
        self._using_custom_registry = "registry"

    def start_metrics_server(self):
        if not self._using_custom_registry:
            print("without problem")


class Provider(AbstractProvider, MetricsMixin):
    def __init__(
        self,
    ):
        super().__init__()

    def get_metadata(self):
        pass

    def resolve_boolean_details(self):
        pass

    def resolve_string_details(self):
        pass

    def resolve_integer_details(self):
        pass

    def resolve_object_details(self):
        pass

    def resolve_float_details(self):
        pass

    async def initialize(self):
        print("Provider initialized.")

        self.start_metrics_server()

        print("Provider shutdown.")


async def main():
    provider = Provider()
    await provider.initialize()


if __name__ == "__main__":
    asyncio.run(main())

Output:

developer@Mhs1kq:/workspaces/python-sdk-provider$ poetry run python -u "/workspaces/python-sdk-provider/test.py"
Provider initialized.
Traceback (most recent call last):
  File "/workspaces/python-sdk-provider/test.py", line 53, in <module>
    asyncio.run(main())
    ~~~~~~~~~~~^^^^^^^^
  File "/usr/local/lib/python3.13/asyncio/runners.py", line 194, in run
    return runner.run(main)
           ~~~~~~~~~~^^^^^^
  File "/usr/local/lib/python3.13/asyncio/runners.py", line 118, in run
    return self._loop.run_until_complete(task)
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/usr/local/lib/python3.13/asyncio/base_events.py", line 720, in run_until_complete
    return future.result()
           ~~~~~~~~~~~~~^^
  File "/workspaces/python-sdk-provider/test.py", line 49, in main
    await provider.initialize()
  File "/workspaces/python-sdk-provider/test.py", line 42, in initialize
    self.start_metrics_server()
    ~~~~~~~~~~~~~~~~~~~~~~~~~^^
  File "/workspaces/python-sdk-provider/test.py", line 11, in start_metrics_server
    if not self._using_custom_registry:
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'Provider' object has no attribute '_using_custom_registry'

@gruebel correctly noted that in this case we have two options. Either put the AbstractProvider at the end of the initialization queue, or explicitly call the initialization of each mixin.

[therb1]

If you add this code to your library(openfeature.provider.provider), the initialization will work as it should.

class FeatureProvider(typing.Protocol):  # pragma: no cover
    def __init__(self):
        super().__init__()

[beeme1mr]

That seems like a reasonable approach but I'll defer to @gruebel.

[GertBurger]

Out of curiosity, what is the purpose of having a mixin with a lower MRO priority than an abstract base class?

Python's MRO (mostly) goes left to right with parent classes and so in practise your base class is almost always on the far right and mixins to the left of it. The more left the mixin is the higher priority it has.

[therb1]

Out of curiosity, what is the purpose of having a mixin with a lower MRO priority than an abstract base class?

Python's MRO (mostly) goes left to right with parent classes and so in practise your base class is almost always on the far right and mixins to the left of it. The more left the mixin is the higher priority it has.

Do you really think that newbies don't write providers? I want to disappoint you, I'm a newbie and I'm writing a provider XD
This is my first ever race condition.

I just thought that if you can protect newbies like me without harming yourself, then it's probably worth it.