[Python] Why is contextlib._RedirectStream implemented as a reentrant context manager?

While reading the code of the _RedirectStream class from the contextlib module, I couldn't understand the purpose of saving the current stdin, stdout, or stderr file into the _old_targets list:

class _RedirectStream(AbstractContextManager):


_stream = None


def __init__(self, new_target):
self._new_target = new_target
# We use a list of old targets to make this CM re-entrant
self._old_targets = []


def __enter__(self):
self._old_targets.append(getattr(sys, self._stream))
setattr(sys, self._stream, self._new_target)
return self._new_target


def __exit__(self, exctype, excinst, exctb):
setattr(sys, self._stream, self._old_targets.pop())


The documentation states that the list is used to make the context manager reentrant. But what's the practical benefit of that in the case of redirecting input or output to a file? In what situation would this be needed?

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