MATLAB: Multiple cause exception handling

exceptionMATLAB

Consider this script,

try
  % code
catch e
  fprintf(1,'Exception identifier: %s\n',e.identifier);
  fprintf(1,'Exception message: %s\n',e.message);
end

When using try & catch to handle exceptions, if exception has multiple causes, it throws something like this:

Exception occurred!
Exception identifier: MATLAB:MException:MultipleErrors
Exception message: Error due to multiple causes.

Any way to parse the exceptions out one-by-one?

Best Answer

Does this help:

R = getReport(e);

? Otherwise check the list in e.cause and display it in a loop.

    ...
  catch ME
    if length(ME.cause) > 1
      for k = 1:length(ME.cause)
        fprintf('Exception message: %s\n', ME.cause{k}.message);
      end
    else
      fprintf('Exception message: %s\n', ME.message);
    end
  end

UNTESTED CODE I cannot run it currently. Maybe you have to adjust it, but I hope the idea got clear.

Related Solutions

MATLAB: Can I throw an empty MException object using THROW, RETHROW, or THROWASCALLER in MATLAB 7.12 (R2011a)

The ability to throw an empty MException object using THROW, RETHROW and THROWASCALLER is not available in MATLAB. To work around this issue, use a condition statement to bypass the use of an empty MException Object:

errobj = MyIsEqual(params)
if isempty(errobj)
  % do nothing
else
  throwAsCaller(errobj)
end

Using condition statements whenever an empty MException object is given, however, may affect the conciseness of the code.

MATLAB: Python from 2014b matlab – debug challanges – where is python stdout, stderr

sys.stdout should be redirected to the MATLAB command window. Do you see output with Python's print function?

Example

>> py.print('hello!')
hello!
>>

sys.stderr is not redirected. When you use the functions print_tb and print_exception, you need to tell the functions to write to sys.stdout.

As a debug tip, the exception you catch in MATLAB due to a Python error is a PyException. The PyException has a property ExceptionObject, which is the same result you get from calling sys.exc_info.

>> try
py.fractions.Fraction(1,0)
catch e
end
>> e
e = 
    PyException with properties:
      ExceptionObject: [1x1 py.tuple]
           identifier: 'MATLAB:Python:PyException'
              message: 'Python Error: both arguments should be Rational instances'
                cause: {}
                stack: [0x1 struct]
>> e.ExceptionObject
ans = 
    Python tuple with no properties.
      (<type 'exceptions.TypeError'>, TypeError('both arguments should be Rational instances',), <traceback object at 0x0000000012AE9A48>)
>> py.traceback.extract_tb(py.operator.getitem(e.ExceptionObject, int32(2)))
ans = 
    Python list with no properties.
      [('C:\\Python27\\lib\\fractions.py', 158, '__new__', 'raise TypeError("both arguments should be "')]
>>

Best Answer

Related Solutions

MATLAB: Can I throw an empty MException object using THROW, RETHROW, or THROWASCALLER in MATLAB 7.12 (R2011a)

MATLAB: Python from 2014b matlab – debug challanges – where is python stdout, stderr

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