In the following test script
-----
class Test:
   def __iter__(self):
      raise IOError

reduce(lambda x,y: x+y, Test())
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the real IOError exception is masked, i.e. the traceback is
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Traceback (most recent call last):
  File "test.py", line 5, in ?
    reduce(lambda x,y: x+y, Test())
TypeError: reduce() arg 2 must support iteration
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but IMHO should be
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Traceback (most recent call last):
  File "test.py", line 3, in ?
          raise IOError
IOError
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This can be fixed by removing the
PyErr_SetString(PyExc_TypeError, "reduce() arg 2 must
support iteration") call in
bltinmodule.c/buildtin_reduce().