Hi,

Please try using below code

class TestComputed(models.Model):

  _name = "test.computed"

    date_field = fields.Date(string='Date')

    quarter_date = fields.Char(string='Quarter and Year', compute='_compute_quarter')

    @api.depends('date_field')

    def _compute_quarter(self):

        for row in self:

            date = row.date_field

            if date:

                year = date.year

                month = date.month

                if month in (1, 2, 3):

                    row.quarter_date = 'Q1 ' + str(year)

                elif month in (4, 5, 6):

                    row.quarter_date = 'Q2 ' + str(year)

                elif month in (7, 8, 9):

                    row.quarter_date = 'Q3 ' + str(year)

                elif month in (10, 11, 12):

                    row.quarter_date = 'Q4 ' + str(year)

                else:

                    row.quarter_date = 'NA'

            else:

                row.quarter_date = 'NA'

Hope it helps