mBot instance has no attribute 'device'

[lukaszrc]

python 2.7.13
Raspberry Pi ver 3 B+

#################################
from lib.mBot import *

def buttonHandling(state):
print "button state: ", state

if name == 'main':
bot = mBot()
bot.startWithSerial("/dev/ttyUSB0")
while(1):
try:
bot.requestButtonOnBoard(1,buttonHandling)
except Exception,ex:
print str(ex)
sleep(0.2)
############################

it gives result:

button state: 1023.0
button state: 1023.0
button state: 1023.0
button state: 1023.0
'callback_128'
Attempting to use a port that is not open
Attempting to use a port that is not open
Attempting to use a port that is not open
Attempting to use a port that is not open
Attempting to use a port that is not open_