Nick Coghlan <[email protected]> added the comment:
The difference here is the one pointed out in the original post: for a
function, you usually only care about having a value, so if you don't want to
call it, you can just swap in a None value instead. If you need an actual
callable, then "lambda:None" fits the bill.
The with statement isn't quite so forgiving. You need a genuine context manager
in order to preserve the correct structure in the calling code. It isn't
intuitively obvious how to do that easily. While not every 3-line function
needs to be in the standard library, sometimes they're worth including to aid
discoverability as much as anything else.
However, I don't see the point in making it a singleton and the name should
include the word "context" so it doesn't becoming ambiguous when referenced
without the module name (there's a reason we went with
contextlib.contextmanager over contextlib.manager).
Something like:
class nullcontext():
"""No-op context manager, executes block without doing any additional
processing.
Used as a standin if a particular block of code is only sometimes
used with a normal context manager:
with optional_cm or nullcontext():
# Perform operation, using the specified CM if one is given
"""
def __enter__():
pass
def __exit__(*exc_info):
pass
----------
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<http://bugs.python.org/issue10049>
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