Modern Python Standard Library Cookbook

Applying variable context managers

When using context managers, you must rely on the with statement to apply them. While it's possible to apply more than one context manager per statement by separating them with commas, it's not as easy to apply a variable number of them:

@contextlib.contextmanager
def first():
    print('First')
    yield

@contextlib.contextmanager
def second():
    print('Second')
    yield

The context managers that we want to apply must be known when writing the code:

>>> with first(), second():
>>>     print('Inside')
First
Second
Inside

But what if sometimes we only want to apply the first context manager, and sometimes we want to apply both?