As Sybrand points out dbms_metadata can be used to generate the souce
as can a full export with no rows plus some edit scripts to extract or
reformat the code.

As Daniel points our a "NOT NULL" is a not null so why not just use the
"nullable" column to always generate a "not null" entry in the create
table? Then you could ignore all type "C" not null constraints.
HTH -- Mark D Powell --