Python subprocess.check_output ()

mystring = subprocess.check_output(["sudo iwlist wlan0 scan"], universal_newlines=True)
word = 'Devsign2G'
print (mystring)
print (word)

if word in str(mystring):
    print ('success')

-сообщение об ошибке-

   Traceback (most recent call last):
      File "test.py", line 52, in 
        mystring = subprocess.check_output(["sudo iwlist wlan0 scan"], universal_newlines=True)
      File "/usr/lib/python2.7/subprocess.py", line 212, in check_output
        process = Popen(stdout=PIPE, *popenargs, **kwargs)
      File "/usr/lib/python2.7/subprocess.py", line 390, in __init__
        errread, errwrite)
      File "/usr/lib/python2.7/subprocess.py", line 1024, in _execute_child
        raise child_exception
    OSError: [Errno 2] No such file or directory

в чем проблема?