Setting the milliseconds property with a value lower or higher will throw an error.
Datetime.milliseconds read/write property
The Datetime.milliseconds property returns a number representing the milliseconds of the moment. Valid values are from 0 through 999.
Setting the milliseconds property with a value lower or higher will throw an error.
Example
-- prints the current number of milliseconds, for example "356"
print(sys.Datetime().milliseconds)