There's no need to use Python 3 for the script and using it introduces
problems due to the poor availability of MySQL Connector/Python for
Python3.
ENUM, SET and DECIMAL values should have a length of -1 as the length is
meaningless for these types.
The schema generator program needs to add the real_type and length fields
if the data types define them.
Also fixed a bug where the real_type and length fields were checked for
generated fields.