ashcatch ashcatch -4 years ago 182
Python Question

Python C API: how to get string representation of exception?

If I do (e.g.)

open("/snafu/fnord")


in Python (and the file does not exist), I get a traceback and the message

IOError: [Errno 2] No such file or directory: '/snafu/fnord'


I would like to get the above string with Python's C API (i.e., a Python interpreter embedded in a C program). I need it as a string, not output to the console.

With
PyErr_Fetch()
I can get the type object of the exception and the value. For the above example, the value is a tuple:

(2, 'No such file or directory', '/snafu/fnord')


Is there an easy way from the information I get from
PyErr_Fetch()
to the string the Python interpreter shows? (One that does not involve to construct such strings for each exception type yourself.)

Answer Source

I think that Python exceptions are printed by running "str()" on the exception instance, which will return the formatted string you're interested in. You can get this from C by calling the PyObject_Str() method described here:

https://docs.python.org/c-api/object.html

Good luck!

Update: I'm a bit confused why the second element being returned to you by PyErr_Fetch() is a string. My guess is that you are receiving an "unnormalized exception" and need to call PyErr_NormalizeException() to turn that tuple into a "real" Exception that can format itself as a string like you want it to.

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