docs: def sign_tx(self, rawtx, wifs):
          """Sign <rawtx> with  given <wifs> as json data.
          <wifs>: '["privatekey_in_wif_format", ...]'
          """
          tx = deserialize.tx(rawtx)
          keys = deserialize.keys(self.testnet, wifs)
          tx = control.sign_tx(self.service, self.testnet, tx, keys)
          return serialize.tx(tx)