嵌套对象的多个上下文管理器函数

Question

我正在使用python 2.7(迁移尚未完成(并尝试构建一个聚合类(集群(，它提供与其单个项目(节点(相同的上下文管理器功能(保留(。理想情况下，我想在不重构所包含对象 Node 的上下文管理器功能的情况下执行此操作。如果它有单独的enter((和exit((方法，也许我会直接在Cluster.reserved((上下文管理器函数中调用它们。但我认为可能有更优雅的方法。我尝试使用ExitStack编写以下代码：

from contextlib import contextmanager
from contextlib2 import ExitStack
class Node:
def __init__(self, id):
self._id = id
@contextmanager
def reserved(self):
print("Node {} reserved".format(self._id))
try:
yield
except:
print("Exception while handling node")
finally:
print("Node released")
def reserve(self):
print("Node {} reserved".format(self._id))
def release(self):
print("Node {} released".format(self._id))
class Cluster:
def __init__(self, id):
self._id = id
self._nodes = [Node(1), Node(2), Node(3), Node(4)]
@contextmanager
def reserved(self):
with ExitStack() as cm:
cm.enter_context(node.reserved() for node in self._nodes)
print("Cluster {} reserved".format(self._id))
try:
yield
except:
print("Exception while handling cluster")
finally:
print("Cluster released")
@contextmanager
def reserved2(self):
with ExitStack() as cm:
for node in self._nodes:
reserve = node.reserve()
cm.callback(node.release(), reserve)
print("Cluster {} reserved".format(self._id))
try:
yield
except:
print("Exception while handling cluster")
finally:
print("Cluster released")
node = Node(10)
with node.reserved():
print('Node {} handled'.format(node._id))

cluster = Cluster(10)
with cluster.reserved2():
print('Cluster {} handled'.format(cluster._id))

第一个函数 reserve(( 返回

AttributeError: type object 'generator' has no attribute '__exit__'

而第二个在保留所有节点后并没有真正产生。想知道处理这个问题的正确方法是什么...

Answer 1

cm.enter_context(node.reserved() for node in self._nodes)

该代码不正确。我应该正确使用列表推导来正确传递上下文管理器对象enter_context