@juleq Thank you for the reply.
I loaded the db1.
how to create a new db2 and hard copy db2?
I managed to copy the message and all other properties but the dump_file failed all the time on :
TypeError: as_dbc_string() missing 1 required positional argument: 'self'

Good job. Maybe I can spot it when you post the failing line and 2-3 lines before it.

@juleq
This is what I used:
########
db = cantools.database.load_file("koko.dbc") ##Loading DBC
db2 = db.get_message_by_frame_id(int(5)) ##Loading specific message number5

create new dbc

db_final = type(db)
db_final.messages = db2
db_final.autosar= autosar
db_final.buses = bus
db_final.nodes = nodes
db_final.dbc = dbc
db_final.version = version
db_final.refresh

dump new dbc

cantools.database.dump_file(db_final, 'bar.dbc')
######################

Thank you :)

Hi @juleq
I managed to work on that :)
by removing the old messages and assign new message :)

Good to hear. Cantools is really useful to eleminate a lot of dbc twiddeling footwork. I also appreciate it for that and just plug it into the build system.