Question

我是编程新手，我哥帮我写了下面的代码。我很难理解为什么您必须设置“int_input = none”，然后说“如果 int_input 不是 None”，非常感谢您的时间！

name = input('What is your name: ' )
int_input = None
string_or_number = input(' Do you want to type in a string or a number? ' )
if string_or_number.upper() == 'NUMBER':
    int_input = int(input(' on a scale of 1-10, how happy are you? ' ))
else:  
    string_input = (input( 'Are you happy or sad? ' ))
if int_input is not None:
    if int_input > 5:
        print("I'm glad to hear you are feeling a " + str(int_input) + ' out of 10')
    elif int_input <=5:
        print("I'm sorry to hear you are feeling a " + str(int_input) + ' out of 10')
else: 
        if string_input.upper() == 'HAPPY':
            print('I am glad you are ' + string_input)
        elif string_input.upper() != 'HAPPY':
            print('That is too bad ' + name) ```

Answer 1

您需要初始化 int_input，因为它后面有 if 语句。

假设您没有初始化 int_input。那么如果 string_or_number.upper() 不等于 'NUMBER'，那么变量 int_input 将永远不会被初始化。所以当你试图在下一个 if 语句中访问它时，即 if int_input > 5:，int_input 不会有值，这会导致 python 解释器抛出一个 NameError，导致代码崩溃。

Answer 2

EL15：通过将 int_input 设置为 None，它为您提供了一种检查用户输入是否被接受或是否正确的方法（在您的情况下，如果它等于 NUMBER ）。例如，如果用户没有输入任何内容或输入错误，那么 int_input 的默认值是 None 并保持不变，因此 if int_input is not None: 中的代码不会运行，而是else 语句中的代码将被执行。

Answer 3

添加到其他答案中，这很好地解释了为什么必须在代码中初始化变量；这是你的代码的不同版本，你不需要初始化这个变量，我现在称之为 hapiness_var，它可以是字符串或整数；但将始终在输入之后定义。

# Input name, remove head/trailing spaces, and turn the first letter into a capital letter.
name = input('What is your name: ' ).strip().capitalize()
# Ask if string or number, remove head/trailing spaces, and then turn into upper cases.
string_or_number = input(' Do you want to type in a string or a number? ' ).strip().upper()

if string_or_number.upper() == 'NUMBER':
    hapiness_var = int(input(' on a scale of 1-10, how happy are you? ' ))
else:
    hapiness_var = input( 'Are you happy or sad? ' ).strip().upper()
    
# Try/except to do see if it's a string or an int.
# If it's a string, the if test will fail, and the program will switch to the
# except clause
try:
    if hapiness_var > 5:
        print (f"I'm glad to hear you are feeling a {hapiness_var} out of 10")
    elif hapiness_var <= 5:
        print("I'm sorry to hear you are feeling a {hapiness_var} out of 10")
except:
    if string_input.upper() == 'HAPPY':
        print('I am glad you are ' + hapiness_var)
    elif string_input.upper() != 'HAPPY':
        print('That is too bad ' + name)

为什么我必须将 int_input 设置为 none？

3 个答案: