Nick Coghlan <ncogh...@gmail.com> added the comment:
To me, this is more a matter of conceptual completeness than one of practical
utility (ala fractions.Fraction). That said, I *have* personally encountered
the "I only sometimes want to wrap this code in a CM" situation, so it isn't
completely impractical, either. Those two factors are enough to reach my
threshold for it being worthwhile to declare "one obvious way to do it" through
the contextlib module.
There is a possible alternative approach that may be more intuitive to use and
read than nullcontext() though:
@contextmanager
def optional_cm(cm, *, use_cm=True): # See naming note below
if cm is None or not use_cm:
yield
else:
with cm:
yield
The OP's original example would then look like:
with optional_cm(transaction):
...
I suspect readers would find it far easier to remember what optional_cm does
than to learn to recognise the "or nullcontext()" idiom. It also plays better
with nested context managers:
with optional_cm(sync_lock), optional_cm(db_transaction), \
open(fname) as f:
...
Naming Note: I nearly suggested "optional_context" as a name for this, but
realised that would be subtly misleading (suggesting PEP 377 style
functionality that potentially skipped the statement body, rather than the
intended semantics of skipping use of the CM)
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue10049>
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