递归地将列表复制到python中的另一个列表 [英] recursively copy a list to another in python

问题描述

我想在python中将列表递归复制到另一个列表.为此，我已将字符串作为输入，定义了一个空列表，并将其作为列表发送给递归函数，以便我可以将该列表复制到另一个列表.但是，错误显示"NoneType"对象没有属性"append". 我想念什么?我已经将"S"定义为main()中的列表. 如果还有其他递归方法，则欢迎使用它们.

I want to copy a list to another recursively in python. For that purpose, i have taken string as input, defined an empty list and send them to recursive function as lists, so that i can copy the list to another list. However, the error displays "NoneType" object has no attribute "append". What am i missing ? i have defined "S" as list in main(). If there are other recursive methods, they are welcomed.

显示错误:

line 35, in string_copy
return string_copy(k,s.append(k[i]),i+1)
AttributeError: 'NoneType' object has no attribute 'append'

代码是:

def string_copy(k,s,i):
  if (i == len(k)):
    return s;
  else:
    return string_copy(k,s.append(k[i]),i+1)


def main():
  print("enter the string you want to copy:");
  k = input();
  s = [None];
  i = 0;
  print("the type of k and s is:", type(k),type(s));
  res = string_copy(list(k),list(s),i);
  print("the desired results are:","\n", res);
if __name__ == "__main__": main()    `       

推荐答案

return string_copy(k,s.append(k[i]),i+1)

列表append()方法不返回更新的列表；它就地添加新项目并返回None.

The list append() method does not return the updated list; it adds the new item in-place and returns None.

因此，下一次对string_copy()的调用将以None作为s的值.

Therefore the next call to string_copy() will have None as the value for s.

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