类型错误:+= 不支持的操作数类型:'NoneType' 和 'str' [英] TypeError: unsupported operand type(s) for +=: 'NoneType' and 'str'

问题描述

我是 Python 新手，我确定我做错了什么 - 我想向用户询问三个数字并打印它们的总和，这是我当前的代码:

I am new to Python and I'm sure that I'm doing something wrong - I would like to ask a user for three numbers and print their sum, here's my current code:

for i in range(0, 3):
    total = None
    num = input('Please enter number {}:'.format(str(i)))
    total += num

顺便说一下，total = None 是为了尝试声明变量，以便我可以在不设置值的情况下使用它?我明白了

By the way, the total = None was to try and declare the variable so I could use it without setting a value? I get this

Traceback (most recent call last):
  File "<pyshell#20>", line 4, in <module>
    total += num
TypeError: unsupported operand type(s) for +=: 'NoneType' and 'str'

推荐答案

你不应该做 total = None.NoneType 不能用于加法.

You shouldn't do total = None. NoneType cannot be used against addition.

错误消息提示了一个额外的问题:根据您的描述，您正在尝试添加 3 个 数字，但内置 input() 的返回类型是str.所以这就是你应该写的:

There's an extra problem suggested by the error message: From your description you're trying to add 3 numbers, but the return type of the builtin input() is str. So this is what you're supposed to write:

total = 0
for i in range(0, 3):
    num = input('Please enter number {}:'.format(str(i)))
    total += int(num)

所有要点:

• 正确缩进代码.缩进是 Python 的关键部分.
• 不要在每次循环时将 total 设置为零.只在循环外设置一次
• 注意类型

• Indent the code correctly. Indentation is a crucial part of Python.
• Don't set total to zero at every loop. Only set it once outside the loop
• Take care of types

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