async def context_a(state: dict = Depends(get_state)):
    state["context_a"] = "started a"
    try:
        yield state
    finally:
        state["context_a"] = "finished a"


async def context_b(state: dict = Depends(context_a)):
    state["context_b"] = "started b"
    try:
        yield state
    finally:
        state["context_b"] = f"finished b with a: {state['context_a']}"

        DirectoryLeaseContext context = new DirectoryLeaseContext(key, leaseState, scope);

        assertEquals(key, context.getLeaseKey());
        assertEquals(leaseState, context.getLeaseState());
        assertEquals(scope, context.getCacheScope());
        assertEquals(30000L, context.getMaxCacheAge());
        assertTrue(context.isNotificationEnabled());
        assertEquals(0, context.getNotificationFilter());
    }

package kms

import (
	"bytes"
	"sort"
	"unicode/utf8"
)

// Context is a set of key-value pairs that
// are associated with a generate data encryption
// key (DEK).
//
// A KMS implementation may bind the context to the
// generated DEK such that the same context must be
// provided when decrypting an encrypted DEK.
type Context map[string]string

// MarshalText returns a canonical text representation of

        @Test
        @DisplayName("Should handle null context in array")
        void testNullContextInArray() {
            CreateContextRequest[] contexts = new CreateContextRequest[4];
            contexts[0] = new MockCreateContextRequest("FIRST");
            contexts[1] = null; // Null context
            contexts[2] = new MockCreateContextRequest("THIRD");
            contexts[3] = new MockCreateContextRequest("FOURTH");

            contexts[2] = new TestCreateContextResponse("CONTEXT3".getBytes(StandardCharsets.UTF_8));

            // Decode each context
            for (int i = 0; i < contexts.length; i++) {
                contexts[i].decode(buffer, i * 100, 50);
            }

            // Verify each context
            for (int i = 0; i < contexts.length; i++) {
                assertNotNull(contexts[i].getName());

/// tip | Dica

Outra forma de criar um gerenciador de contexto é utilizando:

* <a href="https://docs.python.org/3/library/contextlib.html#contextlib.contextmanager" class="external-link" target="_blank">`@contextlib.contextmanager`</a> ou
* <a href="https://docs.python.org/3/library/contextlib.html#contextlib.asynccontextmanager" class="external-link" target="_blank">`@contextlib.asynccontextmanager`</a>

* <a href="https://docs.python.org/zh-cn/3/library/contextlib.html#contextlib.asynccontextmanager" class="external-link" target="_blank">`@contextlib.asynccontextmanager`</a>

使用它们装饰一个只有单个 `yield` 的函数。这就是 **FastAPI** 内部对于 `yield` 依赖项的处理方式。

但是你不需要为FastAPI的依赖项使用这些装饰器（而且也不应该）。FastAPI会在内部为你处理这些。

///

/// note | 技術詳細

以下と一緒に使用できる関数なら何でも有効です:

* <a href="https://docs.python.org/3/library/contextlib.html#contextlib.contextmanager" class="external-link" target="_blank">`@contextlib.contextmanager`</a>または
* <a href="https://docs.python.org/3/library/contextlib.html#contextlib.asynccontextmanager" class="external-link" target="_blank">`@contextlib.asynccontextmanager`</a>

これらは **FastAPI** の依存関係として使用するのに有効です。

実際、FastAPIは内部的にこれら２つのデコレータを使用しています。

```Python
with open("file.txt") as file:
    file.read()
```

Em versões mais recentes do Python, há também um **gerenciador de contexto assíncrono**. Você o usaria com `async with`:

```Python
async with lifespan(app):
    await do_stuff()
```

from collections.abc import AsyncGenerator
from contextlib import AbstractContextManager
from contextlib import asynccontextmanager as asynccontextmanager
from typing import TypeVar

import anyio.to_thread
from anyio import CapacityLimiter
from starlette.concurrency import iterate_in_threadpool as iterate_in_threadpool  # noqa
from starlette.concurrency import run_in_threadpool as run_in_threadpool  # noqa
from starlette.concurrency import (  # noqa