def strfind(sst, st):
    """ find all positions of sst(substring) in st (string)"""
    pos = [[]]
    a = 0
    pos[0] = st.find(sst)
    if pos[0] < 0:
        return pos
    while pos[a] > -1:
        a = a + 1
        pos.append(st.find(sst, pos[a - 1] + 1))
    pos.remove(-1)
    return pos
