All the exceptions that can be thrown by the underlying Tango C++ API are available in the PyTango python module. Hence a user can catch one of the following exceptions:
When an exception is caught, the sys.exc_info() function returns a tuple of three values that give information about the exception that is currently being handled. The values returned are (type, value, traceback). Since most functions don’t need access to the traceback, the best solution is to use something like exctype, value = sys.exc_info()[:2] to extract only the exception type and value. If one of the Tango exceptions is caught, the exctype will be class name of the exception (DevFailed, .. etc) and the value a tuple of dictionary objects all of which containing the following kind of key-value pairs:
1 2 3 4 5 6 7 8 | import PyTango
# How to protect the script from exceptions raised by the Tango
try:
# Get proxy on a non existing device should throw an exception
device = DeviceProxy("non/existing/device")
except DevFailed as df:
print("Failed to create proxy to non/existing/device:\n%s" % df)
|
The C++ PyTango::Except class with its most important methods have been wrapped to Python. Therefore, in a Python device server, you have the following methods to throw, re-throw or print a Tango::DevFailed exception :
The following code is an example of a command method requesting a command on a sub-device and re-throwing the exception in case of:
1 2 3 4 5 6 7 | try:
dev.command_inout("SubDevCommand")
except PyTango.DevFailed as df:
PyTango.Except.re_throw_exception(df,
"MyClass_CommandFailed",
"Sub device command SubdevCommand failed",
"Command()")
|
line 2: | Send the command to the sub device in a try/catch block |
---|---|
line 4-6: | Re-throw the exception and add a new level of information in the exception stack |
Bases: Boost.Python.instance
A containner for the static methods:
- throw_exception
- re_throw_exception
- print_exception
- compare_exception
Print all the details of a TANGO error stack.
Parameters:
ex: (PyTango.DevErrorList) The error stack reference
Print all the details of a TANGO exception.
Parameters:
ex: (PyTango.DevFailed) The DevFailed exception
Parameters:
ex: (PyTango.DevFailed) The DevFailed exception reason: (str) The exception DevError object reason field desc: (str) The exception DevError object desc field origin: (str) The exception DevError object origin field sever: (PyTango.ErrSeverity) The exception DevError object severity field Throws:
Generate and throw a TANGO DevFailed exception. The exception is created with a single DevError object. A default value PyTango.ErrSeverity.ERR is defined for the DevError severity field.
The parameters are the same as the ones generates by a call to sys.exc_info().
Parameters:
type: (class) the exception type of the exception being handled value: (object) exception parameter (its associated value or the second argument to raise, which is always a class instance if the exception type is a class object) traceback: (traceback) traceback object Throws: New in PyTango 7.2.1
Generate a TANGO DevFailed exception. The exception is created with a single DevError object. A default value PyTango.ErrSeverity.ERR is defined for the DevError severity field.
The parameters are the same as the ones generates by a call to sys.exc_info().
Parameters : |
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Return : | (PyTango.DevFailed) a tango exception object |
New in PyTango 7.2.1
Bases: Boost.Python.instance
Structure describing any error resulting from a command execution, or an attribute query, with following members:
- reason : (str) reason
- severity : (ErrSeverity) error severty (WARN, ERR, PANIC)
- desc : (str) error description
- origin : (str) Tango server method in which the error happened
Bases: exceptions.Exception
Bases: PyTango.DevFailed
This exception is thrown when a problem occurs during the connection establishment between the application and the device. The API is stateless. This means that DeviceProxy constructors filter most of the exception except for cases described in the following table.
The desc DevError structure field allows a user to get more precise information. These informations are :
- DB_DeviceNotDefined
- The name of the device not defined in the database
- API_CommandFailed
- The device and command name
- API_CantConnectToDevice
- The device name
- API_CorbaException
- The name of the CORBA exception, its reason, its locality, its completed flag and its minor code
- API_CantConnectToDatabase
- The database server host and its port number
- API_DeviceNotExported
- The device name
Bases: PyTango.DevFailed
This exception is thrown when a communication problem is detected during the communication between the client application and the device server. It is a two levels Tango::DevError structure. In case of time-out, the DevError structures fields are:
Level Reason Desc Severity 0 API_CorbaException CORBA exception fields translated into a string ERR 1 API_DeviceTimedOut String with time-out value and device name ERR For all other communication errors, the DevError structures fields are:
Level Reason Desc Severity 0 API_CorbaException CORBA exception fields translated into a string ERR 1 API_CommunicationFailed String with device, method, command/attribute name ERR
Bases: PyTango.DevFailed
This exception has only one level of Tango::DevError structure. The possible value for the reason field are :
- API_UnsupportedProtocol
- This error occurs when trying to build a DeviceProxy or an AttributeProxy instance for a device with an unsupported protocol. Refer to the appendix on device naming syntax to get the list of supported database modifier
- API_UnsupportedDBaseModifier
- This error occurs when trying to build a DeviceProxy or an AttributeProxy instance for a device/attribute with a database modifier unsupported. Refer to the appendix on device naming syntax to get the list of supported database modifier
- API_WrongDeviceNameSyntax
- This error occurs for all the other error in device name syntax. It is thrown by the DeviceProxy class constructor.
- API_WrongAttributeNameSyntax
- This error occurs for all the other error in attribute name syntax. It is thrown by the AttributeProxy class constructor.
- API_WrongWildcardUsage
- This error occurs if there is a bad usage of the wildcard character
Bases: PyTango.DevFailed
This exception has only one level of Tango::DevError structure. The reason field is set to API_NonDatabaseDevice. This exception is thrown by the API when using the DeviceProxy or AttributeProxy class database access for non-database device.
Bases: PyTango.DevFailed
This exception has only one level of Tango::DevError structure. The possible value for the reason field are :
- API_EmptyDbDatum
- This error occurs when trying to extract data from an empty DbDatum object
- API_IncompatibleArgumentType
- This error occurs when trying to extract data with a type different than the type used to send the data
- API_EmptyDeviceAttribute
- This error occurs when trying to extract data from an empty DeviceAttribute object
- API_IncompatibleAttrArgumentType
- This error occurs when trying to extract attribute data with a type different than the type used to send the data
- API_EmptyDeviceData
- This error occurs when trying to extract data from an empty DeviceData object
- API_IncompatibleCmdArgumentType
- This error occurs when trying to extract command data with a type different than the type used to send the data
Bases: PyTango.DevFailed
This exception is thrown by the API layer when a request to a feature implemented in Tango device interface release n is requested for a device implementing Tango device interface n-x. There is one possible value for the reason field which is API_UnsupportedFeature.
Bases: PyTango.DevFailed
This exception is thrown by the API layer when a the asynchronous model id badly used. This exception has only one level of Tango::DevError structure. The possible value for the reason field are :
- API_BadAsynPollId
- This error occurs when using an asynchronous request identifier which is not valid any more.
- API_BadAsyn
- This error occurs when trying to fire callback when no callback has been previously registered
- API_BadAsynReqType
- This error occurs when trying to get result of an asynchronous request with an asynchronous request identifier returned by a non-coherent asynchronous request (For instance, using the asynchronous request identifier returned by a command_inout_asynch() method with a read_attribute_reply() attribute).
Bases: PyTango.DevFailed
This exception is thrown by the API layer when:
- a request to get asynchronous reply is made and the reply is not yet arrived
- a blocking wait with timeout for asynchronous reply is made and the timeout expired.
There is one possible value for the reason field which is API_AsynReplyNotArrived.
Bases: PyTango.DevFailed
This exception is thrown by the API layer when subscribing or unsubscribing from an event failed. This exception has only one level of Tango::DevError structure. The possible value for the reason field are :
- API_NotificationServiceFailed
- This error occurs when the subscribe_event() method failed trying to access the CORBA notification service
- API_EventNotFound
- This error occurs when you are using an incorrect event_id in the unsubscribe_event() method
- API_InvalidArgs
- This error occurs when NULL pointers are passed to the subscribe or unsubscribe event methods
- API_MethodArgument
- This error occurs when trying to subscribe to an event which has already been subsribed to
- API_DSFailedRegisteringEvent
- This error means that the device server to which the device belongs to failed when it tries to register the event. Most likely, it means that there is no event property defined
- API_EventNotFound
- Occurs when using a wrong event identifier in the unsubscribe_event method
Bases: PyTango.DevFailed
This exception is thrown by the API layer when a device locked by the process has been unlocked by an admin client. This exception has two levels of Tango::DevError structure. There is only possible value for the reason field which is
- API_DeviceUnlocked
- The device has been unlocked by another client (administration client)
The first level is the message reported by the Tango kernel from the server side. The second layer is added by the client API layer with informations on which API call generates the exception and device name.
Bases: PyTango.DevFailed
Bases: Boost.Python.instance
This exception is only thrown by the DeviceProxy::write_attributes() method. In this case, it is necessary to have a new class of exception to transfer the error stack for several attribute(s) which failed during the writing. Therefore, this exception class contains for each attributes which failed :
- The name of the attribute
- Its index in the vector passed as argumen tof the write_attributes() method
- The error stack