How to avoid nested "with" statements when working with multiple files in Python

Question

When working with multiple files in Python code can get ugly when using the recommended style:

with open("foo.txt") as foo:
    with open("bar.txt", "w") as bar:
         with open("baz.txt", "w") as baz:
              # Read from foo, write different output to bar an baz

That's three indentation levels just for working with files! The alternative would be this

foo = open("foo.txt")
bar = open("bar.txt", "w")
baz = open("baz.txt", "w")
# Read from foo, write different output to bar an baz
foo.close()
bar.close()
baz.close()

I have a feeling that either of these examples could be refactored to something more elegant. Any examples?

Answer 1

Python 2.7 and up let you specify multiple context managers in one with statement:

with open("foo.txt") as foo, open("bar.txt", "w") as bar, open("baz.txt", "w") as baz:
    # Read from foo, write different output to bar an baz

The line does get long, and you cannot use parentheses to keep that below 80 characters. You can use \ backslash continuations however:

with open("foo.txt") as foo,\
        open("bar.txt", "w") as bar,\
        open("baz.txt", "w") as baz:
    # Read from foo, write different output to bar an baz

Another option would be to use contextlib.ExitStack() context manager (only in Python 3.3 and up):

from contextlib import ExitStack

with ExitStack() as stack:
    foo = stack.enter_context(open("foo.txt"))
    bar = stack.enter_context(open("bar.txt"))
    baz = stack.enter_context(open("baz.txt"))