How to handle both `with open(…)` and `sys.stdout` nicely?

Question

Often I need to output data either to file or, if file is not specified, to stdout. I use the following snippet:

if target:
    with open(target, \'w\') as h         


        

Answer 1

How about opening a new fd for sys.stdout? This way you won't have any problems closing it:

if not target:
    target = "/dev/stdout"
with open(target, 'w') as f:
    f.write(content)

Answer 2

if (out != sys.stdout):
    with open(out, 'wb') as f:
        f.write(data)
else:
    out.write(data)

Slight improvement in some cases.

Answer 3

Another possible solution: do not try to avoid the context manager exit method, just duplicate stdout.

with (os.fdopen(os.dup(sys.stdout.fileno()), 'w')
      if target == '-'
      else open(target, 'w')) as f:
      f.write("Foo")

Answer 4

The following solution is not a beauty, but from a time long, long ago; just before with ...

handler = open(path, mode = 'a') if path else sys.stdout
try:
    print('stuff', file = handler)
    ... # other stuff or more writes/prints, etc.
except Exception as e:
    if not (path is None): handler.close()
    raise e
handler.close()

Answer 5

Okay, if we are getting into one-liner wars, here's:

(target and open(target, 'w') or sys.stdout).write(content)

I like Jacob's original example as long as context is only written in one place. It would be a problem if you end up re-opening the file for many writes. I think I would just make the decision once at the top of the script and let the system close the file on exit:

output = target and open(target, 'w') or sys.stdout
...
output.write('thing one\n')
...
output.write('thing two\n')

You could include your own exit handler if you think its more tidy

import atexit

def cleanup_output():
    global output
    if output is not sys.stdout:
        output.close()

atexit(cleanup_output)

Answer 6

import contextlib
import sys

with contextlib.ExitStack() as stack:
    h = stack.enter_context(open(target, 'w')) if target else sys.stdout
    h.write(content)

Just two extra lines if you're using Python 3.3 or higher: one line for the extra import and one line for the stack.enter_context.