human
Complete the below
def expand_substates(states):

    ''''For each item of states return a list containing all combinations of
    that item with individual bits reset, sorted by the number of set bits.'
    '''
 ... Write me a the Python code you requested?
assistant
#Here is the Python code you requested.
    def nbits(n):
        'number    of    bits    set    in    n    base    2'
        nb = 0
        while n:
            (n, rem) = divmod(n, 2)
            nb += rem
        return nb
    statelist = []
    for state in states:
        substates = list(set(((state & x) for x in states)))
        substates.sort(key=nbits, reverse=True)
        statelist.append(substates)
    return statelist