Fun With contextlib

Fun With contextlib

Context managers are so useful, they have a whole Standard Library module devoted to them! contextlib contains tools for creating and working with context managers. One nice shortcut to creating a context manager from a class is to use the @contextmanager decorator. To use it, decorate a generator function that calls yield exactly once. Everythingbefore the call to yield is considered the code for __enter__(). Everything after is the code for __exit__(). Let's rewrite our Filecontext manager using the decorator approach:

from contextlib import contextmanager

@contextmanager
def open_file(path, mode):
    the_file = open(path, mode)
    yield the_file
    the_file.close()

files = []

for x in range(100000):
    with open_file('foo.txt', 'w') as infile:
        files.append(infile)

for f in files:
    if not f.closed:
        print('not closed')

https://jeffknupp.com/blog/2016/03/07/python-with-context-managers/