code: def prog(self, prog):
          
          self.argparser.prog = prog
          fmt = '%s %%s' % prog if prog else '%s'
          for command in self.subcommands.values():
              command.prog = fmt % command.name
          # Rebind autoenv vars with recomputed key.
          for action in self._autoenv_actions:
              self.argparser.unbind_env(action)
              self.argparser.bind_env(action, self._make_autoenv(action))
docs: Update ourself and any of our subcommands.