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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def bind_env(self, action, env):
 """ Bind an environment variable to an argument action. The env value will traditionally be something uppercase like `MYAPP_FOO_ARG`. Note that the ENV value is assigned using `set_defaults()` and as such it will be overridden if the argument is set via `parse_args()` """

        if env in self._env_actions:
            raise ValueError('Duplicate ENV variable: %s' % env)
        self._env_actions[env] = action
        action.env = env