How to simplify this kind of Python code?

Question

I have many blocks of code like this:

try:
  a = get_a()
  try:
    b = get_b()

    # varying codes here, where a and b are used

  finally:
    if b:
      cleanup(b)
finally:
  if a:
    cleanup(a)

I hope to write some magic code like this:

some_magic:
  # varying codes here, where a and b are also available

Is this possible?

Why not merge them both inside a single try and finally? — legends2k
– legends2k, Commented Mar 9, 2016 at 10:06

Ilya Popov · Accepted Answer · 2016-03-09 10:10:11Z

5

If you can't or don't want to implement context protocol for a and b, you can use contextlib facilities to make a context:

from contextlib import contextmanager

@contextmanager
def managed(a):
    try:
        yield a
    finally:
        if a:
            cleanup(a)

with managed(get_a()) as a, managed(get_b()) as b:
    # do something here
    pass

answered Mar 9, 2016 at 10:10

Ilya Popov

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1 Comment

Antti Haapala Over a year ago

upvoted (was about to write that after hunting references)

Community · Accepted Answer · 2017-05-23 12:15:30Z

3

Let classes of a and b implement the context manager protocol, and use the with statement:

with get_a() as a, get_b() as b:
    do_magic

Now if get_a and get_b returned open file handles, they'd be automatically closed at the end of the block. If the values returned are of a custom class, that class should have the __enter__ and __exit__ magic methods.

edited May 23, 2017 at 12:15

CommunityBot

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answered Mar 9, 2016 at 10:10

Antti Haapala

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