Are you sure this can't return a different value? How does the following behave?

class Evil:
    _len = 10
    def __getitem__(self, x):
        if 0 <= x < self._len: return 1
        raise IndexError  # needed to make list(Evil()) work
    def __len__(self, x):
        self._len -= 1
        return self._len

I went down a rabbit hole here and ended up at gh-13407. As an interesting side effect, this allows iterators to be passed as a shape:

np.zeros(i*i for i in range(5))

Hehe, there you think something is easy. But yeah, I had somehow forgotten to think length might change :). I will check your changes today, seems like it doubles as nice maintenance at least. Closing this, as we will probably end up with that.