Conditional with statement in Python

Question

Is there a way to begin a block of code with a with statement, but conditionally?

Something like:

if needs_with():
    with get_stuff() as gs:

# do          


        

Answer 1

As of Python 3.7 you can use contextlib.nullcontext:

from contextlib import nullcontext

if needs_with():
    cm = get_stuff()
else:
    cm = nullcontext()

with cm as gs:
    # Do stuff

contextlib.nullcontext is pretty much just a no-op context manager. You can pass it an argument that it will yield, if you depend on something existing after the as:

>>> with nullcontext(5) as value:
...     print(value)
...
5

Otherwise it'll just return None:

>>> with nullcontext() as value:
...     print(value)
...
None

It's super neat, check out the docs for it here: https://docs.python.org/3/library/contextlib.html#contextlib.nullcontext

Answer 2

A third-party option to achieve exactly this:
https://pypi.python.org/pypi/conditional

from conditional import conditional

with conditional(needs_with(), get_stuff()):
    # do stuff