code: def delete_by_user_name(user_name):
          '''
          Delete user in the database by `user_name`.
          '''
          try:
              del_count = TabMember.delete().where(TabMember.user_name == user_name)
              del_count.execute()
              return True
          except:
              return Falsf delete_by_user_name(user_name):
          '''
          Delete user in the database by `user_name`.
          '''
          try:
              del_count = TabMember.delete().where(TabMember.user_name == user_name)
              del_count.execute()
              return True
          except:
              return False
docs: Delete user in the database by `user_name`.