Hi,

you can use

@api.onchange('<field whose value to be taken>')

def onchange_func(self):

if self.<field value to be taken>:

self.  <field to which you need value> = self.<field  whose value to be taken>

You can achieve that by this one-liner, note though that the value of the other field should be created afore:

display_name = fields.Char(string='Display Name', default=lambda self: self.name, translate=True)