Can I catch error codes when using Fabric to run() calls in a remote shell?

Question

Normally Fabric quits as soon as a run() call returns a non-zero exit code. For some calls, however, this is expected. For example, PNGOut returns an error code of 2 when it is unable to compress a file.

Currently I can only circumvent this limitation by either using shell logic (do_something_that_fails || true or do_something_that_fails || do_something_else), but I'd rather be able to keep my logic in plain Python (as is the Fabric promise).

Is there a way to check for an error code and react to it rather than having Fabric panic and die? I still want the default behaviours for other calls, so changing its behaviour by modifying the environment doesn't seem like a good option (and as far as I recall, you can only use that to tell it to warn instead of dying anyway).

Answer 1

You can prevent aborting on non-zero exit codes by using the settings context manager and the warn_only setting:

from fabric.api import settings

with settings(warn_only=True):
    result = run('pngout old.png new.png')
    if result.return_code == 0: 
        do something
    elif result.return_code == 2: 
        do something else 
    else: #print error to user
        print result
        raise SystemExit()

Update: My answer is outdated. See comments below.