For Python2.7 - modifying MYGz's answer to not strip milliseconds:
from datetime import datetime
d = datetime.strptime("20.12.2016 09:38:42,76", "%d.%m.%Y %H:%M:%S,%f").strftime('%s.%f')
d_in_ms = int(float(d)*1000)
print(d_in_ms)
print(datetime.fromtimestamp(float(d)))
Output:
1482248322760
2016-12-20 09:38:42.760000