datetime.datetime.fromtimestamp(ms/1000.0)
from datetime import datetime
print(datetime.utcnow().strftime('%Y-%m-%d %H:%M:%S.%f')[:-3])
from datetime import datetime
dt_obj = datetime.strptime('20.12.2016 09:38:42,76',
'%d.%m.%Y %H:%M:%S,%f')
millisec = dt_obj.timestamp() * 1000
print(millisec)