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Comment by davidwf | Hacker News Reader

I write a lot of Python and didn't know about this despite it being a 2015 blog post! The real kicker for me is:

* [ExitStack] easily scales up to many resources (including a dynamic number that's acquired in a loop)

In particular ExitStacks are useful when you have 0 or 1 resources. It allows a sort of null-context manager for when the number of resources you have to allocate might be 0.

Do be aware that https://docs.python.org/3.9/library/contextlib.html#contextl... also exists as of 3.7 -- you can do

  ctx_mgr = foo() if bar else nullcontext()
  with ctx_mgr:
      ...

if you like.

Or even, from Python 3.8:

    with (ctx_mgr := foo() if bar else nullcontext()):
        ...

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