[New-bugs-announce] [issue42424] add constructor that support multiple context managers to contextlib.ExitStack and contextlib.AsyncExitStack

[Vito De Tullio]

New submission from Vito De Tullio <vito.detullio at gmail.com>:

The enhancement is to add a __init__ method to both contextlib.ExitStack and contextlib.AsyncExitStack, so that you can pass (async)context managers directly in the costructor.

additionally, a new "context_managers" / "async_context_managers" field is added to retrieve the values passed


This will ease the usage with lists of context managers

instead of:

    with ExitStack() as stack:
        files = [stack.enter_context(open(fname)) for fname in filenames]

you can have

    with ExitStack(*(open(fname) for fname in filenames)) as stack:
        files = stack.context_managers

In my use case I have a fixed + variable number of (async)context managers, and I don't even need the "as" part

   ...
   in_send, in_receive = trio.open_memory_channel(0)
   out_sends, out_receives = [], []
   for _ in range(n): # n is dynamic
       out_send, out_receive = trio.open_memory_channel(0)
       out_sends.append(out_send)
       out_receives.append(out_receive)
   
   # syntax error
   async with in_send, in_receive, *out_sends, *out_receives:
       ...

   # with current AsyncExitStack
   async with AsyncExitStack() as stack:
       await stack.async_context_managers(in_send)
       await stack.async_context_managers(in_receive)
       for out_send in out_sends:
           await stack.async_context_managers(out_send)
       for out_receive in out_receives:
           await stack.async_context_managers(out_receives)
       ...

   # with the change
   async with AsyncExitStack(in_send, in_receive, *out_sends, *out_receives):
       ...

----------
components: Library (Lib)
messages: 381561
nosy: ZeD
priority: normal
severity: normal
status: open
title: add constructor that support multiple context managers to contextlib.ExitStack and contextlib.AsyncExitStack
type: enhancement

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue42424>
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