code: def get_user(self, username):
          
          User = get_user_model()
          try:
              user = User.objects.get(**{
                  User.USERNAME_FIELD: username,
              })
              if user.is_active:
                  raise ActivationError(
                      self.ALREADY_ACTIVATED_MESSAGE,
                      code='already_activated'
                  )
              return user
          except User.DoesNotExist:
              raise ActivationError(
                  self.BAD_USERNAME_MESSAGE,
                  code='bad_username'
              )
docs: Given the verified username, look up and return the
          corresponding user account if it exists, or raising
          ``ActivationError`` if it doesn't.