Multiple variables in Python 'with' statement

Question

Is it possible to declare more than one variable using a with statement in Python?

Something like:

from __future__ import with_statement

with open("out.txt","wt"), open("in.txt") as file_out, file_in:
    for line in file_in:
        file_out.write(line)

... or is cleaning up two resources at the same time the problem?

Answer 1

I think you want to do this instead:

from __future__ import with_statement

with open("out.txt","wt") as file_out:
    with open("in.txt") as file_in:
        for line in file_in:
            file_out.write(line)

Answer 2

See http://docs.python.org/library/contextlib.html -- contextlib.nested supports this use. I.e.:

import contextlib

with contextlib.nested(open("out.txt","wt"), open("in.txt")) as (file_out, file_in):

   ...

which is very close to your desired usage.

Answer 3

why not just:

with open(out_file, 'w') as file:
    file.writelines(open(in_file))

Answer 4

open('out.txt', 'w').writelines(open('in.txt'))

Both files will be implicity, immediately closed just after execution of this line, in CPython.

Answer 5

It is possible now, in Python 3.1. The new with syntax supports multiple context managers:

with A() as a, B() as b, C() as c:
    doSomething(a,b,c)

Unlike the contextlib.nested, this guarantees that a and b will have their __exit__()'s called even if C() or it's __enter__() method raises an exception.

Update: Now coming to a Python 2.7 interpreter near you!