newnext is replacing exceptions raised inside iterator.__next__()

[dphoyes]

Failing test case:

from builtins import *
import unittest

def my_generator():
    yield None.some_var

class TestCase(unittest.TestCase):
    def test(self):
        with self.assertRaises(AttributeError):
            next(my_generator())

unittest.main()

Under Python3, this passes. Under Python2 without the builtins import, this passes. Under Python2, using newnext as provided by the builtins import, we get this failure:

Traceback (most recent call last):
  File "/home/davhoy01/tmp/futurebug.py", line 10, in test
    next(my_generator())
  File "/usr/lib/python2.7/dist-packages/future/builtins/newnext.py", line 62, in newnext
    iterator.__class__.__name__))
TypeError: 'generator' object is not an iterator

This is caused by the fact that newnext is trying to catch the AttributeError resulting from a non-existent __next__ attribute, and replacing the exception with a TypeError exception. But it's also inadvertently catching any AttributeError raised from inside the call to __next__, which ought to instead be propagated normally.