[Python-bugs-list] [ python-Bugs-665761 ] reduce() masks exception

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Bugs item #665761, was opened at 2003-01-10 09:41
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=105470&aid=665761&group_id=5470

Category: Python Interpreter Core
Group: None
Status: Open
Resolution: None
Priority: 3
Submitted By: Walter Dörwald (doerwalter)
Assigned to: Nobody/Anonymous (nobody)
Summary: reduce() masks exception

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

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


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Comment By: Jp Calderone (kuran)
Date: 2003-01-11 12:08

Message:
Logged In: YES 
user_id=366566

the __iter__ method is supposed to return an object that
defines a 'next' method.  The returned object is the one
used for iteration, not the original.  So I believe the
error message is correct - Test does not support iteration.
 If you change the code to:

>>> class test:
...   def __iter__(self):
...     return self
...   def next(self):
...     raise IOError
... 
>>> reduce(operator.add, test())

You get the expected result...

Traceback (most recent call last):
&nbsp;&nbsp;File "<stdin>", line 1, in ?
&nbsp;&nbsp;File "<stdin>", line 5, in next
IOError


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