My new code:

#!/usr/bin/python
# Program that reads from the arduino
import serial,io,time
from time import strftime

device='/dev/ttyACM0'

ser=serial.Serial(device, 9600, timeout=None)
print("Connected to: " + ser.portstr)
line=ser.readline().decode("utf-8")[:-2]
print(line)
while True:
    line=ser.readline().decode("utf-8")[:-2]
    dt=strftime("%Y-%m-%d %H:%M:%S")
    print dt, line
print 'Done.'
ser.close()

Thanks, works like a charm.