pythonic equivalent of Mathematica's FixedPoint function

[jelle]

>You could probably write your own FixedPoint function without too much
>difficulty, with the only tricky part being for it to know when to
stop!

It would be quite interesting to have this kind of function. But
likely its far from trivial.
FixedPoint seems to be one of the core functions in Mathematica, where
many other functions are based on. Some additions such as FixedPoint
would make functional programming in Python more functional is suppose.
Or would anyone consider it sugar syntax for ??