Python Subprocess Hang

python_subprocess_hang

testCmd = "/sbin/iptables -n -L %s"

# <snip>

def checkChain():

    cmd = testCmd % chain

    check = subprocess.Popen(cmd,
                             shell=True,
                             stdout=subprocess.PIPE,
                             stderr=subprocess.PIPE)

    # I don't know why, but check.stdout.read() needs to be given to something
    # or the whole thing freezes
    check_stdout = check.stdout.read()

    check_error = check.stderr.read()
    if check_error:
        print (check_error + "\n")  
    else:
        print "No errors"