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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 signMsg(self, msg: Dict, identifier: Identifier=None, otherIdentifier: Identifier=None):
 """ Creates signature for message using specified signer :param msg: message to sign :param identifier: signer identifier :param otherIdentifier: :return: signature that then can be assigned to request """

        idr = self.requiredIdr(idr=identifier or otherIdentifier)
        signer = self._signerById(idr)
        signature = signer.sign(msg)
        return signature