Get subprocess error output from shell command

[Chris Rebert]

On Sat, Apr 2, 2011 at 9:03 PM, Benjamin Kaplan
<benjamin.kaplan at case.edu> wrote:
> On Sat, Apr 2, 2011 at 11:50 PM, Gnarlodious <gnarlodious at gmail.com> wrote:
>> I get it, you instantiate an object, call a method and get a tuple in
>> response. However, here is what I see:
>>
>>>>> process.communicate()
>> (b'~/Library/Preferences/iCab/iCab 4 Bookmarks: Permission denied\n',
>> b'')
>>
>> So all I get is the string and no error message, which is the same
>> thing I get with the simpler subprocess.call(). I can parse out the
>> error out and handle it if I need to. Is this a failing in the OSX
>> plutil tool?
>
> Were you expecting a Python error? That's not how POSIX shells work. A
> process that fails just gives you a non-zero return code, not an
> exception. You can call process.poll() to get the return code.

However, using subprocess.check_call() or subprocess.check_output()
will cause a non-zero exit code to raise a Python exception,
CalledProcessError.
http://docs.python.org/library/subprocess.html#subprocess.check_call
http://docs.python.org/library/subprocess.html#subprocess.check_output

Cheers,
Chris