python from 2014b matlab - debug challanges - where is python stdout, stderr?
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Chris Barnhart
il 18 Gen 2015
Commentato: Chris
il 21 Gen 2015
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?
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Robert Snoeberger
il 20 Gen 2015
Modificato: Robert Snoeberger
il 20 Gen 2015
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 "')]
>>
3 Commenti
Robert Snoeberger
il 21 Gen 2015
Debugging will be very difficult without a valid matlab.exception.PyException class. The message says that matlab.exception.PyException contains a parse error or cannot be found. Use the which function to see if can be found.
>> which matlab.exception.PyException
C:\Program Files\MATLAB\R2014b\toolbox\matlab\external\interfaces\python\+matlab\+exception\PyException.m % matlab.exception.PyException constructor
>>
If it is found, then try to create a PyException to check for a parse error.
>> e = matlab.exception.PyException('MATLAB:Py:Test', 'testing', [])
e =
PyException with properties:
ExceptionObject: []
identifier: 'MATLAB:Py:Test'
message: 'testing'
cause: {}
stack: [0x1 struct]
>>
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