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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 cancel_all(self, product_id=None):
 """ With best effort, cancel all open orders. Args: product_id (Optional[str]):
 Only cancel orders for this product_id Returns: list: A list of ids of the canceled orders. Example:: [ "144c6f8e-713f-4682-8435-5280fbe8b2b4", "debe4907-95dc-442f-af3b-cec12f42ebda", "cf7aceee-7b08-4227-a76c-3858144323ab", "dfc5ae27-cadb-4c0c-beef-8994936fde8a", "34fecfbf-de33-4273-b2c6-baf8e8948be4" ] """

        if product_id is not None:
            params = {'product_id': product_id}
        else:
            params = None
        return self._send_message('delete', '/orders', params=params)