Python，无法将 input() 转换为 int()

我正在尝试使用以下代码将 input() 数据转换为 int() ：

prompt_text = "Enter a number: "
try:
  user_num = int(input(prompt_text))
except ValueError:
  print("Error")

for i in range(1,10):
  print(i, " times ", user_num, " is ", i*user_num)

even = ((user_num % 2) == 0)

if even:
  print(user_num, " is even")
else:
  print(user_num, " is odd")

当我输入时出现以下奇怪的错误asd2例如：

Enter a number: asd2 Error 
Traceback (most recent call last):   File "chapter3_ex1.py", line 8, in <module>
    print(i, " times ", user_num, " is ", i*user_num) 
NameError: name 'user_num' is not defined

我究竟做错了什么？

您面临的问题是解释器在try并执行except堵塞。之后它将开始执行每一行。这将抛出NameError

您可以通过将程序的其余部分放入else block.

prompt_text = "Enter a number: "

try:
    user_num = int(input(prompt_text))  

except ValueError:
    print("Error")

else:
    for i in range(1,10):
      print(i, " times ", user_num, " is ", i*user_num)

    even = ((user_num % 2) == 0)

    if even:
      print(user_num, " is even")
    else:
      print(user_num, " is odd")

引用自Python教程

try ... except 语句有一个可选的 else 子句，其中，当 存在，必须遵循所有例外条款。对于以下代码很有用 必须是如果 try 子句没有引发异常则执行.

另一种方法是使用sentinel value

prompt_text = "Enter a number: "
user_num = 0 # default value
try:
    user_num = int(input(prompt_text))
except ValueError:
    print("Error")

这也会起作用。然而结果可能并不如预期。

Protip - 使用 4 个空格缩进