In the attached file there are two tiny functions, flatten1() and
flatten2(). There is only one difference between them:
flatten1() has the line:
    if isinstance(x, list):
and flatten2() has this line instead:
    if isinstance(x, collections.Sequence):

flatten1() works perfectly in Python 2.5.1 and Python 30a2 (just comment
out the flatten2() code).
But flatten2() goes into "infinite" recursion in Python 30a2 when trying
to flatten list "c".