Sometimes I need a dummy context manager that does nothing. It can then be used as a stand-in for a more useful, but optional, context manager. For example:
ctx_mgr = <meaningfulContextManager> if <condition> else <nullContextManager>
with ctx_mgr:
...
How do I define such a trivial, empty context manager? Does the Python library offer one off the shelf?
How about cases where we want the context to be used with an as clause?
with ctx_mgr as resource:
<operations on resource>
A simple solution for Python 3.6 and below, including 2.7:
from contextlib import contextmanager
@contextmanager
def nullcontext(enter_result=None):
yield enter_result
Since Python 3.7 you should use the provided contextlib.nullcontext instead.
Since Python 3.2, memoryview(b'') can be use as a no-op context manager. See https://docs.python.org/3/library/stdtypes.html#memoryview.release.
Pros
No imports required
Works on 3.2+
Roughly twice as fast as contextlib.nullcontext
Cons
# no-op comment.Simple solution for Python 2.7, not yet mentioned in the answers:
from contextlib import nested
with nested():
...
For Python 2.7+ , you can use
import contextlib
with (lambda noop_func: contextlib.contextmanager(noop_func))(lambda: (yield))():
print("hi")
I just used threading.Lock() as a dummy context manager. Temporary lock, only used by the context manager.