Question

我已经编写了下面的Python代码（实际上，这是我在“24小时内自学Python”第80页的练习解决方案。）

这个想法是：桌子周围有4个座位，服务员知道每个座位的订购量，输入4个金额并得到总数。

如果提供的raw_input不是一个数字（但是一个字符串），我的代码将该人踢出去。然而，目标是给出错误消息（“此条目无效”）并再次请求输入 - 直到它是数字。但是，我无法弄清楚如何再次询问用户原始输入 - 因为我已经在循环中。

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

通常，当您不知道要运行循环的次数时，解决方案是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

正如Patrick Haugh和SilentLupin所说，while循环可能是最好的方法。另一种方式是递归 - 即，一遍又一遍地调用相同的函数，直到获得有效的输入：

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!"

在上面的代码中，get_valid_input一遍又一遍地调用自己，直到其中一个提供的validators产生了一些真实的东西。

如何在循环内发出警告并再次询问raw_input

3 个答案: