gistfile1.txt

def perm1c(lst):
    """A modification of perm1b to return a copied list instead of modified in place"""
    initial = lst[:]
    yield lst 
    lst = lst[:]

    if len(lst) == 1: return

    n = len(lst) - 1
    while 1:
        j = n - 1
        while lst[j] >= lst[j+1]:
            j -= 1
            #because this algorithm iterates in lexicographic order,
            #we know that lst is reverse sorted right now
            #if j == -1: return #terminate
            if j == -1:
                lst.reverse()
                if lst == initial: #if lst was sorted to begin with
                    return
                yield lst
                lst = lst[:]
                j = n-1
                break
        l = n
        while lst[j] >= lst[l]:
            l -= 1
        lst[j], lst[l] = lst[l], lst[j]
        k = j + 1
        l = n
        while k < l:
            lst[k], lst[l] = lst[l], lst[k]
            k += 1
            l -= 1
        if lst == initial:
            return
        yield lst
        lst = lst[:]