human
Solve the following python programming problem given the following code:
def mock_streams(which) : 
    "
    Replaces a stream with a ``StringIO`` during the test, then restores after.

    Must specify which stream (stdout, stderr, etc) via string args, e.g.::

        @mock_streams('stdout')
        def func():
            pass

        @mock_streams('stderr')
        def func():
            pass

        @mock_streams('both')
        def func()
            pass

    If ``'both'`` is specified, not only will both streams be replaced with
    StringIOs, but a new combined-streams output (another StringIO) will appear
    at ``sys.stdall``. This StringIO will resemble what a user sees at a
    terminal, i.e. both streams intermingled.
    " 
    both = (which == 'both') 
    stdout = ((which == 'stdout') or both) 
    stderr = ((which == 'stderr') or which) 
    def mocked_streams_decorator(func) : 
        @ wraps (func) 
        def inner_wrapper(* args, **kwargs) : 
            if both : 
                sys.stdall = StringIO () 
                fake_stdout = CarbonCopy (cc = sys.stdall) 
                fake_stderr = CarbonCopy (cc = sys.stdall) 
else : 
                (fake_stdout, fake_stderr) = (StringIO (), StringIO ()) 
if stdout : 
                (my_stdout, sys.stdout) = (sys.stdout, fake_stdout) 
if stderr : 
                (my_stderr, sys.stderr) = (sys.stderr, fake_stderr) 
try : 
                ret = func (* args, ** kwargs) 
finally : 
                if stdout : 
                    sys.stdout = my_stdout 
if stderr : 
                    sys.stderr = my_stderr 
if both : 
                    del sys.stdall 
return inner_wrapper 
return mocked_streams_decorator 

    
    

    Fix the buggy line: stderr = ((which == 'stderr') or which)
assistant
#Here is Python program to fix the buggy line: stderr = ((which == 'stderr') or which)
.

stderr = ((which == 'stderr') or both)