code: def check_unique_attr(self, attrs, user=None, form=None, flash_msg=None):
          
          user = user or self.current
          ucol = self.options["username_column"]
          email = self.options["email_column"]
          if not isinstance(attrs, (list, tuple, dict)):
              attrs = [attrs]
  
          for name in attrs:
              if isinstance(attrs, dict):
                  value = attrs[name]
              else:
                  form = form or current_context.data.get("form")
                  if not form:
                      raise OptionMissingError("Missing 'value' option or form in 'check_user_unique_attr' action")
                  value = form[name].data
  
              if name == ucol and not self.options["username_case_sensitive"]:
                  filters = (ucol + '_lcase', value.strip().lower())
              elif name == emailcol:
                  filters = (emailcol, value.strip().lower())
              else:
                  filters = (name, value.strip())
  
              if self.query.filter({"$and": [filters, ("id__ne", user.id)]}).count() > 0:
                  if flash_msg is None:
                      flash_msg = "The %s is already in use" % name
                  if flash_msg:
                      flash(flash_msg, "error")
                  current_context.exit(trigger_action_group="user_attr_not_unique")
docs: Checks that an attribute of the current user is unique amongst all users.
          If no value is provided, the current form will be used.