在 python 中结合 with 语句和 for 循环

Question

Consider the following python code which uses a context manager to acquire and release a resource:

from contextlib import contextmanager

@contextmanager
def res(i):
    print(f'Opening resource {i}')
    yield
    print(f'Closing resource {i}')

Now assume that we need to use a couple of those resources

with res(0), res(1), res(2):
    print('Using resources.')

where the inner part depends on all the three resources being open simultaneously. After running the code above, we get the expected output:

Opening resource 0
Opening resource 1
Opening resource 2
Using resources.
Closing resource 2
Closing resource 1
Closing resource 0

If you have to use even more resources - res(0)... res(10) is it possible to dynamically generate using a for loop the equivalent of the pseudo code below?

with res(0), res(1), ... , res(10):
    print('Using resources.')

Answer 1

This is what contextlib.ExitStack is for.

with ExitStack() as es:
    for x in range(10):
        es.enter_context(res(x))

Each context manager in the stack will be exited in the reverse order they were entered, once the with statement completes.