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

2014bprint outputpythonstdout

When running python from 2014b matlab, where does the output from the python program go?
The greater problem is I'm at a loss as to how to debug my python script. It runs well outside of matlab, but has started to fail when run inside matlab in an seemingly un-tracable manner as it has grown. I've added extra exception handlers, but can't see the output.
 except :
    exc_type, exc_value, exc_traceback = sys.exc_info()
    traceback.print_tb(exc_traceback, limit=1, file=sys.stdout)
    traceback.print_exception(exc_type, exc_value, exc_traceback, limit=5, file=sys.stdout)
(I'll change that file=sys.stdout to a real file which can help)
Any debug tips, or where I can find stdout?

Best Answer

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 "')]
>>
Related Question