如何在循环内发出警告并要求输入raw_input

Question

我已经在下面编写了Python代码（实际上它是我在第24页的“在24小时内自学Python”练习的解决方案）。

想法是：餐桌周围有4个座位，服务员知道每个座位的订购量，输入这4个数量并获得总数。

如果提供的raw_input不是一个数字（而是一个字符串），我的代码会将这个人踢出去。但是，目标是给出错误消息（“此条目无效”）并再次询问输入 - 直到它为数字。但是，我无法弄清楚如何再次询问用户的原始输入 - 因为我已经在循环中了。

非常感谢您的建议！

def is_numeric(value): 
    try: 
    input = float(value) 
    except ValueError: 
    return False 
    else: 
    return True 


total = 0 
for seat in range(1,5): 

    print 'Note the amount for seat', seat, 'and' 
    myinput = raw_input("enter it here ['q' to quit]: ") 

    if myinput == 'q': 
    break 

    elif is_numeric(myinput): 
    floatinput = float(myinput) 
    total = total + floatinput 

    else: 
    print 'I\'m sorry, but {} isn\'t valid. Please try again'.format(myinput) 
    break 

if myinput == 'q': 
    print "Goodbye!" 
else: 
    total = round(total, 2) 
    print "*****\nTotal: ${}".format(total) 
    print "Goodbye!" 

Answer 1

一般情况下，当你不知道要多少次运行循环的解决方案是一个while循环。

for seat in range(1,5): 
    my_input = raw_input("Enter: ") 
    while not(my_input == 'q' or isnumeric(my_input)): 
     my_input = raw_imput("Please re-enter value") 
    if my_input == 'q': 
     break 
    else: 
     total += float(my_input) 

Answer 2

total = 0 
for seat in range(1,5): 
    incorrectInput = True 
    while(incorrectInput): 
     print 'Note the amount for seat', seat, 'and' 
     myinput = raw_input("enter it here ['q' to quit]: ") 

     if myinput == 'q': 
      print 'Goodbye' 
      quit() 

     elif is_numeric(myinput): 
      floatinput = float(myinput) 
      total = total + floatinput 
      incorrectInput = False 

     else: 
      print 'I\'m sorry, but {} isn\'t valid. Please try again'.format(myinput) 


total = round(total, 2) 
print "*****\nTotal: ${}".format(total) 
print "Goodbye!" 

Answer 3

帕特里克霍先生和SilentLupin建议，一个while循环可能是最好的办法。另一种方式是recursion-即遍地调用同一个功能，直到你得到一个有效的输入：

def is_numeric(value): 
    try: 
    input = float(value) 
    except ValueError: 
    return False 
    else: 
    return True 

def is_q(value): 
    return value == 'q' 

def is_valid(value, validators): 
    return any(validator(input) for validator in validators) 

def get_valid_input(msg, validators): 
    value = raw_input(msg) 
    if not is_valid(value, validators): 
    print 'I\'m sorry, but {} isn\'t valid. Please try again'.format(value) 
    value = get_valid_input(msg, validators) 
    return value 

total = 0 
for seat in range(1,5): 

    print 'Note the amount for seat', seat, 'and' 
    myinput = get_valid_input("enter it here ['q' to quit]: ", [is_q, is_numeric]) 

    if myinput == 'q': 
    break 

    elif is_numeric(myinput): 
    floatinput = float(myinput) 
    total = total + floatinput 

if myinput == 'q': 
    print "Goodbye!" 
else: 
    total = round(total, 2) 
    print "*****\nTotal: ${}".format(total) 
    print "Goodbye!" 

在上面的代码，get_valid_input电话本身一遍又一遍，直到供应validators之一产生什么truthy。