检测输入是int还是str•Python 2.7

Question

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编程一个程序，它会告诉你，如果你足够大，可以投票。而且，当它询问你的年龄时，如果用户输入的是字母而不是数字，我希望它能说某件事，例如“请输入数字，而不是字母，重新启动”。这里是我现在所拥有的代码：

name = raw_input("What is your name?: ") 
print("") 
print("Hello, "+name+".\n") 
print("Today we will tell you if you are old enough to vote.") 
age = input("How old are you?: ") 
if age >= 18: 
    print("You are old enough to vote, "+name+".") 
elif age < 18: 
    print("Sorry, but you are not old enough to vote, "+name+".") 

Answer 1

你可以尝试这样的事情：

name = raw_input("What is your name?: ") 
print("") 
print("Hello, "+name+".\n") 
print("Today we will tell you if you are old enough to vote.") 
while True: 
    try: 
     #get the input to be an integer. 
     age = int(raw_input("How old are you?: ")) 
     #if it is you break out of the while 
     break 
    except ValueError: 
     print("Please enter a number, not a letter. Restart.") 
if age >= 18: 
    print("You are old enough to vote, "+name+".") 
elif age < 18: 
    print("Sorry, but you are not old enough to vote, "+name+".") 

Answer 2

name = raw_input("What is your name?: ") 
print("") 
print("Hello, "+name+".\n") 
print("Today we will tell you if you are old enough to vote.") 
while True: 
    age = raw_input("How old are you?: ") 
    try: 
     age = int(age) 
    except ValueError: 
     print("Please enter a number, not a letter. Restart.") 
    else: 
     break 
if age >= 18: 
    print("You are old enough to vote, "+name+".") 
elif age < 18: # else: 
    print("Sorry, but you are not old enough to vote, "+name+".") 

在try-except-else，我们尽量年龄将从字符串为整数。如果发生ValueError，则意味着输入字符串不是合法的整数。如果没有，那么我们可以跳出while循环并执行以下任务。

注意1：最好不要在python2中使用input()。请参阅this。

注2：elif是没用的。只需使用else即可。