除了ValueError之外的Python : While True

Question

我尝试使用'while true‘来要求用户输入0或一个正整数。我尝试了几种不同的方法，它们似乎都有不同的问题。函数def positive_int拒绝字母和负整数，但不允许阶乘函数工作。阶乘函数独立工作。我得到一个错误代码: TypeError:不支持的操作数类型+：'NoneType‘和'int’，此行的I in range(1，num + 1)：。谢谢你的帮助。

def positive_int(prompt=''):
     while True:
         try:
             num = int(input(prompt))
             if num < 0:
                 raise ValueError
             break
         except ValueError:
             print("Please enter a positive integer.")     

print('\n')    
print("The program will compute and output the factorial number.")
def factorial():
        num = positive_int('Please enter the number to factorial: ')
        factorial = 1
        if num == 0:
           print("\nThe factorial of 0 is 1")
        else:
           for i in range(1,num + 1):
               factorial = factorial*i
           print("\nThe factorial of", num,"is",factorial)  
factorial()

Answer 1

positive_int()函数不返回任何内容，这意味着num = positive_int()将num设置为None。稍后，当代码尝试将此None值添加到一个整数时，它会失败。

您可以通过将break语句替换为return或在中断循环后返回num来解决此问题：

def positive_int(prompt=''):
     while True:
         try:
             num = int(input(prompt))
             if num < 0:
                 raise ValueError
             return num  # Replacing break with return statement 
         except ValueError:
             print("Please enter a positive integer.") 

或

def positive_int(prompt=''):
     while True:
         try:
             num = int(input(prompt))
             if num < 0:
                 raise ValueError
             break
         except ValueError:
             print("Please enter a positive integer.") 

     return num  # Breaking out of the loop takes you here

Answer 2

您同时将factorial用作函数名和变量名。

Answer 3

问题是positive_int没有返回任何内容

尝试：

def positive_int(prompt=''):
     while True:
         try:
             num = int(input(prompt))
             if num < 0:
                 raise ValueError

             return num  # change to return value rather than break
         except ValueError:
             print("Please enter a positive integer.")     

print('\n')    
print("The program will compute and output the factorial number.")
def factorial():
        num = positive_int('Please enter the number to factorial: ')
        factorial = 1
        if num == 0:
           print("\nThe factorial of 0 is 1")
        else:
           for i in range(1,num + 1):
               factorial = factorial*i
           print("\nThe factorial of", num,"is",factorial)  
factorial()