code: def company_business_id(self):
          
          def calculate_checksum(number):
              """Calculate the checksum using mod 11,2 method"""
              factors = [7, 9, 10, 5, 8, 4, 2]
              sum_ = 0
              for x, y in zip(number, factors):
                  sum_ = sum_ + int(x) * y
              if sum_ % 11 == 0:
                  return '0'
              else:
                  return str(11 - sum_ % 11)
  
          first_digit = str(self.random_digit_not_null())
          body = first_digit + self.bothify('######')
          cs = calculate_checksum(body)
          return body + '-' + str(cs)
docs: Returns Finnish company Business Identity Code (y-tunnus).
          Format is 8 digits - e.g. FI99999999,[8] last digit is a check
          digit utilizing MOD 11-2. The first digit is zero for some old
          organizations. This function provides current codes starting with
          non-zero.