我該如何循環這個

Question

對Python來說很新穎，我使用2.7來編寫腳本。

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

我需要循環 - 如果輸入是字母數字或字母，它應該再次要求輸入。

我似乎無法找到一種方法在它的while循環中滑動。

（Python的新手，請善待！）

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' 循環永遠，阻止它的唯一辦法是循環