def findall(string,sub):
    """Starting indices of all occuenreces of a substring within a string.
    E.g. findall("Allowed Hello Hollow","ll") -> [1,10,16]"""
    indices = []
    if len(sub) > 0:
        index = 0 - len(sub)
        while True:
            index = string.find(sub,index+len(sub))
            if index == -1: break
            indices += [index]
    return indices