On Thu, Jun 29, 2017 at 6:50 AM, Steven D'Aprano <st...@pearwood.info> wrote:
> try:
> something
> except:
> exc_type, exc, tb = sys.exc_info()
> print(traceback.extract_tb(tb))
> raise
>
> Why does it return the exception type separately from the exception, when
> the type can be derived by calling `type(exc)`?
I think normally it is redundant. While the type and value do have to
be tracked separately for the thread's hot exception state (i.e.
curexc_type, curexc_value, curexc_traceback), sys.exc_info() returns a
caught exception (i.e. exc_type, exc_value, exc_traceback), which is
normalized by PyErr_NormalizeException.
In CPython you can trivially force the exception value to be None by
calling PyErr_SetExcInfo. For example:
import sys
import ctypes
PyErr_SetExcInfo = ctypes.pythonapi.PyErr_SetExcInfo
PyErr_SetExcInfo.restype = None
PyErr_SetExcInfo.argtypes = (ctypes.py_object,) * 3
PyErr_SetExcInfo(TypeError, None, None)
>>> sys.exc_info()
(<class 'TypeError'>, None, None)
Of course this is a silly example, because C.
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