Hi

Do you mean you would like to record the country_id that has been assigned to your model?

e.g. First when "Belgium" is selected, sequence_field will show "Belgium" and after "Canada" is select, sequence_field will show "Belgium Canada"?

If this is the case, you many try to make the sequence_field  a compute field.

Example

Class TempTemp(models.Model)

    _name = 'temp.temp'

    country_id = fields.Many2one('res.country','Country')

    sequence_field = fields.Char(compute='_get_sequence')

    @api.depends('country_id')
    def _get_sequence(self):
        self.sequence_field += self.country_id.name