If the whole operation fails, for instance if the server is busy or malfunctioning, or if the client request is badly formatted, the server responds with a SOAP Fault message, which contains a detailed error description.
SOAP Faults are caught by the ZSI framework. This way PyOPC can raise an OPC specific Python error, the OPCServerError. The OPCServerError inherits from ZSI's Fault error and contains the SOAP faultcode, the faultstring and the detail. More information about SOAP faults can be found in [SEE02] or [LIV02].