code: def is_member_of(self, group_dn):
          
          is_member = None
  
          # Normalize the DN
          group_dn = group_dn.lower()
  
          # If we have self._group_dns, we'll use it. Otherwise, we'll try to
          # avoid the cost of loading it.
          if self._group_dns is None:
              is_member = self._group_type.is_member(self._ldap_user, group_dn)
  
          if is_member is None:
              is_member = group_dn in self.get_group_dns()
  
          logger.debug(
              "{} is{}a member of {}".format(
                  self._ldap_user.dn, is_member and " " or " not ", group_dn
              )
          )
  
          return is_member
docs: Returns true if our user is a member of the given group.