context-managers.md

This page describes how to work with Rodi and context managers.

How Rodi handles context managers

When a class implements the context manager protocol (__enter__, __exit__), Rodi instantiates the class but does not enter nor exit the instance automatically.

from rodi import Container


class A:
    def __init__(self) -> None:
        print("A created")
        self.initialized = False
        self.disposed = False

    def __enter__(self) -> "A":
        print("A initialized")
        self.initialized = True
        return self

    def __exit__(self, exc_type, exc_val, exc_tb) -> None:
        self.disposed = True
        print("A destroyed")


class B:
    def __init__(self, dependency: A) -> None:
        self.dependency = dependency

    def do_work(self):
        with self.dependency:
            print("Do work")


container = Container()

container.register(A)
container.register(B)

b = container.resolve(B)

# b.dependency is instantiated and provided as is, it is not entered
# automatically
assert b.dependency.initialized is False
assert b.dependency.disposed is False

b.do_work()
assert b.dependency.initialized is True
assert b.dependency.disposed is True

/// admonition | Rodi does not enter and exit contexts. type: into

There is no way to unambiguously know the intentions of the developer: should a context be entered automatically and disposed automatically? ///

Async context managers

As described above for context managers, Rodi does not handle async context managers in any special way either.

import asyncio

from rodi import Container


class A:
    def __init__(self) -> None:
        print("A created")
        self.initialized = False
        self.disposed = False

    async def __aenter__(self) -> "A":
        print("A initialized")
        self.initialized = True
        return self

    async def __aexit__(self, exc_type, exc_val, exc_tb) -> None:
        self.disposed = True
        print("A destroyed")


class B:
    def __init__(self, dependency: A) -> None:
        self.dependency = dependency

    async def do_work(self):
        async with self.dependency:
            print("Do work")


container = Container()

container.register(A)
container.register(B)

b = container.resolve(B)
assert b.dependency.initialized is False
assert b.dependency.disposed is False


asyncio.run(b.do_work())
assert b.dependency.initialized is True
assert b.dependency.disposed is True

The next page describes support for Union types in Rodi.