How to loop until state is unchanged in python

Question

I often find I want to repeat a block of code until some state stops changing. As an example, suppose rects is a list of rectangles and rect is a single rectangle and we want to keep merging rect with rectangles from rects, enlarging rect each time, until there's nothing overlapping:

stable = False
while not stable:
   stable = True
   for rect2 in list(rects):
      if rect.overlaps(rect2):
         rect = rect.merge(rect2)
         rects.remove(rect2)
         stable = False

In Haskell, we have this natural solution https://stackoverflow.com/a/7443379/125940 . What is the most natural way to achieve this in Python? I came up with this:

class DoUntilStable:
    def __init__(self):
        self._stable = False

    def __iter__(self):
        while not self._stable:
            self._stable = True
            yield self

    def changed(self):
        self._stable = False

for dus in DoUntilStable():
   for rect2 in list(rects):
      if rect.overlaps(rect2):
         dus.changed()
         rect = rect.merge(rect2)
         rects.remove(rect2)