The reason of computed fields is been used is because it defines a filed whose value is computed rather then simply being read from the database.
Below are the attributes that are specific to computed fields. To define such a field, simply provide a value for the attribute compute and records value. For example you can seen the below code.

 upper = fields.Char(compute='_compute_upper',
                    inverse='_inverse_upper',
                    search='_search_upper')

@api.depends('Demo')
def _compute_upper(self):
    for rec in self:
        rec.upper = rec.name.upper() if rec.name else False

def _inverse_upper(self):
    for rec in self:
        rec.name = rec.upper.lower() if rec.upper else False

def _search_upper(self, operator, value):
    if operator == 'like':
        operator = 'ilike'
    return [('Demo', operator, value)]
     self.pname = self.partner_id.name

Note- Acomputed field is not stored to the database.