Christophe,

It looks like your patch goes out of its way to avoid creating nested partials.  This is a worthwhile goal and I think it should be done in partial_new so that partial(partial(f, x), y) returns partial(f, x, y).

If fact, I was surprised to learn that current partial implementation does not behave this way:

>>> partial(partial(f, 1), 2).func
<functools.partial object at 0x100435af8>

Does anyone know the reason for the current behavior?  It is possible that I am missing some subtlety related to keyword arguments.