python 函数报错TypeError: object of type 'int' has no len()

函数源码

_times = 0
def hannuota(nlist,mfrom,mpass,mto):
    global _times
    n=len(nlist)
    #n=nlist._length_
    if n==1:
        _times+=1
        print('%-2d'%_times,nlist[0],':',mfrom,'------>',mto)
    else:
        hannuota(nlist[:n-1],mfrom,mto,mpass)
        hannuota(nlist[-1],mfrom,mpass,mto)
        hannuota(nlist[:n-1],mpass,mfrom,mto)


if __name__=='__main__':
    print('the process is as following:\n')
    print('step   num:from------>to')
    hannuota([0,1,2],'A','B','C')
~

运行时报错：

the process is as following:

step   num:from------>to
('1 ', 0, ':', 'A', '------>', 'C')
Traceback (most recent call last):
  File "hannuota.py", line 18, in 
    hannuota([0,1,2],'A','B','C')
  File "hannuota.py", line 10, in hannuota
    hannuota(nlist[:n-1],mfrom,mto,mpass)
  File "hannuota.py", line 11, in hannuota
    hannuota(nlist[-1],mfrom,mpass,mto)
  File "hannuota.py", line 4, in hannuota
    n=len(nlist)
TypeError: object of type 'int' has no len()

问题出在“hannuota(nlist[-1],mfrom,mpass,mto)”，nlist[-1]是一个int类型。log中已经指明出错行数了。

 改正后的代码为：

_times = 0
def hannuota(nlist,mfrom,mpass,mto):
    global _times
    n=len(nlist)
    #n=nlist._length_
    if n==1:
        _times+=1
        print('%-2d'%_times,nlist[0],':',mfrom,'------>',mto)
    else:
        hannuota(nlist[:n-1],mfrom,mto,mpass)
        hannuota([nlist[-1]],mfrom,mpass,mto)
        hannuota(nlist[:n-1],mpass,mfrom,mto)


if __name__=='__main__':
    print('the process is as following:\n')
    print('step   num:from------>to')
    hannuota([0,1,2],'A','B','C')
~

运行结果：

the process is as following:

step   num:from------>to
('1 ', 0, ':', 'A', '------>', 'C')
('2 ', 1, ':', 'A', '------>', 'B')
('3 ', 0, ':', 'C', '------>', 'B')
('4 ', 2, ':', 'A', '------>', 'C')
('5 ', 0, ':', 'B', '------>', 'A')
('6 ', 1, ':', 'B', '------>', 'C')
('7 ', 0, ':', 'A', '------>', 'C')