## Gerenciadores de contexto

### O que são gerenciadores de contexto

"Gerenciadores de Contexto" são qualquer um dos objetos Python que podem ser utilizados com a declaração `with`.

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']}"

  // Set up distributed execution environment on local and remote tasks.
  // When `reset_context` is true, initialize new cluster context state based
  // on cluster configurations provided in `server_def`; otherwise, update
  // existing context state with the provided `server_def`. Contexts created
  // on remote tasks will be considered stale and garbage collected after
  // `keep_alive_secs` of inactivity.

			content.StorageClass = filterStorageClass(ctx, object.StorageClass)
		} else {
			content.StorageClass = globalMinioDefaultStorageClass
		}
		content.Owner = owner
		contents = append(contents, content)
	}
	data.Name = bucket
	data.Contents = contents

	data.EncodingType = encodingType
	data.Prefix = s3EncodeName(prefix, encodingType)
	data.Marker = s3EncodeName(marker, encodingType)

			t.Fatal(err)
		}
		nextFiles = next
	}

	for _, c := range contexts {
		c.Compiler = build.Default.Compiler
	}

	walkers := make([]*Walker, len(contexts))
	var wg sync.WaitGroup
	for i, context := range contexts {
		i, context := i, context
		wg.Add(1)
		go func() {
			defer wg.Done()
			walkers[i] = NewWalker(context, filepath.Join(testenv.GOROOT(t), "src"))
		}()
	}
	wg.Wait()

	})
	return remoteVersionID(res.VersionID), s3.ToObjectError(err, object)
}

func (s3 *warmBackendS3) Put(ctx context.Context, object string, r io.Reader, length int64) (remoteVersionID, error) {
	return s3.PutWithMeta(ctx, object, r, length, map[string]string{})
}

func (s3 *warmBackendS3) Get(ctx context.Context, object string, rv remoteVersionID, opts WarmBackendGetOpts) (io.ReadCloser, error) {
	gopts := minio.GetObjectOptions{}

}

namespace tensorflow {
namespace {
class CustomDeviceAPI : public tensorflow::CustomDevice {
 public:
  CustomDeviceAPI(TFE_Context* context, TFE_CustomDevice device, void* info,
                  string name)
      : context_(context), device_(device), info_(info), name_(name) {}

  ~CustomDeviceAPI() override { device_.delete_device(info_); }

  const string& name() override { return name_; }

        op_outputs_ = std::vector<TensorHandlePtr>();
        Execute(context_, operation_name_, std::move(op_inputs_), attributes_,
                expected_max_outputs_, &op_outputs_, status_.get());
        execution_state_ = ExecutionState::kHasResult;
      }
    }
    finished_execute_.notify_one();
  }
}

void DeviceThread::StartExecute(TFE_Context* context,
                                const char* operation_name,

	return val
}

func setCaller(ctx context.Context, cl *RemoteClient) context.Context {
	//nolint:staticcheck // SA1029 Staticcheck is drunk.
	return context.WithValue(ctx, ctxCallerKey{}, cl)
}

func setSubroute(ctx context.Context, s string) context.Context {
	//nolint:staticcheck // SA1029 Staticcheck is drunk.
	return context.WithValue(ctx, ctxSubrouteKey{}, s)
}

```Python
with open("./somefile.txt") as f:
    contents = f.read()
    print(contents)
```

Underneath, the `open("./somefile.txt")` creates an object that is called a "Context Manager".

When the `with` block finishes, it makes sure to close the file, even if there were exceptions.

When you create a dependency with `yield`, **FastAPI** will internally create a context manager for it, and combine it with some other related tools.