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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 unset_env(self, key):
 """Removes an environment variable using the prepended app_name convention with `key`."""

        os.environ.pop(make_env_key(self.appname, key), None)
        self._registered_env_keys.discard(key)
        self._clear_memoization()