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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 list_versions(self, app_id):
 """List the versions of an app. :param str app_id: application ID :returns: list of versions :rtype: list[str] """

        response = self._do_request(
            'GET', '/v2/apps/{app_id}/versions'.format(app_id=app_id))
        return [version for version in response.json()['versions']]