任意の数のコンテキストマネージャを作る

code:before.py

with foo() as a:

with bar() as b:

with baz() as c:

...

code:after.py

with ExitStack() as stack:

contexts = [stack.enter_context(f()) for f in foo, bar, baz

...

実際は AsyncExitStack のほうが使う機会があるかな?

async with ... で await enter_async_context(...) する

code:langgraph.py

async def make_graph():

async with AsyncExitStack() as st:

sessions = [

await st.enter_async_context(mcp_client.session(server))

for server in server_names

]

tools = sum(await asyncio.gather(*map(load_mcp_tools, sessions)), [])

yield create_react_agent(model=model, tools=tools)