为什么我的代码不能进入循环？

Question

def is_number(s): 
    try: 
     float(s) 
     return True 
    except ValueError: 
     return False 


flag = True 
while flag != False: 
    numInput = raw_input("Enter your first number: ") 
    if is_number(numInput): 
     numInput = float(numInput) 
     flag = True 
     break 
    else: 
     print "Error, only numbers are allowed" 

我看不到问题。
为什么它不进入一个循环？
不打印什么，只是被卡住。

Answer 1

flag = False这里不需要：

else: 
    print "Error, only numbers are allowed" 
    flag = False <--- remove this 

只需使用：

while True: 
    numInput = raw_input("Enter your first number: ") 
    if is_number(numInput): 
     numInput = float(numInput) 
     break 
    else: 
     print "Error, only numbers are allowed" 

演示：

Enter your first number: foo 
Error, only numbers are allowed 
Enter your first number: bar 
Error, only numbers are allowed 
Enter your first number: 123 

Answer 2

试试这个：

while True: 
    numInput = raw_input("Enter your first number: ")  
    try: 
     numInput = float(numInput) 
     break 
    except: 
     print "Error, only numbers are allowed"