我该如何循环这个

Question

对Python来说很新颖，我使用2.7来编写脚本。

a = raw_input("Input number or decimal only") 
Try: 
    Y = float(a) 
    print a 
except ValueError: 
    print "wrong input, try again" 

我需要循环 - 如果输入是字母数字或字母，它应该再次要求输入。

我似乎无法找到一种方法在它的while循环中滑动。

（Python的新手，请善待！）

Answer 1

correct = False 
a = "" 
while not correct: 
    a = raw_input("Input number or decimal only") 
    correct = a.isalnum() 
    if not correct: 
     print "wrong input, try again" 
print a 

Answer 2

input = "%" # Set to be non alphanumeric so loop starts 
while not input.isalnum(): 
    input = raw_input("Input number or decimal only > ") 
    if not input.isalnum(): 
     print ("Invalid Input, try again") 
    else: 
     print (input) 

Answer 3

while True: # Loops! 
    a = raw_input("Input number or decimal only\n") 
    try: 
     Y = float(a) 
     print a 
     break # Interrupts the loop if the input was a number 
    except ValueError: 
     print "wrong input, try again" 

'而真正的' 循环永远，阻止它的唯一办法是循环