Oops, it doesn't reverse decreasing runs. Make that:

    import operator as op
    import itertools as it
    
    def mono_split(cmp, lst):
        start = len(list(it.takewhile(lambda t: cmp(t[0], t[1]), zip(lst, lst[1:]))))
        return lst[:start + 1], lst[start + 1:]
    
    def get_mono_splits(lst):
        while len(lst) >= 2:
            if lst[0] == lst[1]:
                yield [lst[0]]
                lst = lst[1:]
            else:
                cmp = op.lt if lst[0] < lst[1] else op.gt
                run, lst = mono_split(cmp, lst)
                if cmp == op.gt:
                    run = list(reversed(run))
                yield run
        if len(lst) == 1:
            yield lst