if i call
clob = cursor.var(cx_Oracle.CLOB)
cursor.execute('begin :res = mbank.test_null(); end;', res = clob);
everything works fine
Another way is to let cx_Oracle close everything at end of scope (i.e remove your close calls), since it knows the order to do it. Regardless, the next cx_Oracle release will use ODPI-C 2.2 which handles this all better and has done away with DPI-1054 errors.
well, it's not solution...
while using connection pool on server i need to close connections if they are too old. So there is no end of scope for them...
P.s. thanks, waiting for release...