'Retrieves information about an HSM. You can identify the HSM
by its ARN or its serial number.
:type hsm_arn: string
:param hsm_arn: The ARN of the HSM. Either the HsmArn or the
SerialNumber parameter must be specified.
:type hsm_serial_number: string
:param hsm_serial_number: The serial number of the HSM. Either the
HsmArn or the HsmSerialNumber parameter must be specified.'

def describe_hsm(self, hsm_arn=None, hsm_serial_number=None):

    params = {}
    if (hsm_arn is not None):
        params['HsmArn'] = hsm_arn
    if (hsm_serial_number is not None):
        params['HsmSerialNumber'] = hsm_serial_number
    return self.make_request(action='DescribeHsm', body=json.dumps(params))
