Question

我正在尝试编写一个接受数字输入的脚本，然后检查以查看

（a）输入实际上是一个数字，和（b）有关数目少于或等于17。

我尝试了各种各样的“if”语句无济于事，现在我试图围绕“尝试”语句。这是我迄今为止最好的尝试：

def listlength():
    print "How many things (up to 17) do you want in the list?"
    global listlong
    listlong = raw_input("> ")
    try:
        listlong = int(listlong)
        listlong <= 17
    except:
        print "Gotta be a number less than 17, chumpy!"
        listlength()
    liststretcher()

它适用于try中的第一个元素：如果它不是数字，我必须再次运行listlength函数。但是完全忽略了第二个元素（＆lt; = 17）。

我也试过

try:
    listlong = int(listlong) and listlong <= 17

...但是这仍然只给我一个功能性的第一次检查，并完全忽略了第二次。

如果我有两个try语句，我也会得到相同的结果：

    try:
        listlong = int(listlong)
    except:
        print "Gotta be a number, chumpy!"
        listlength()
    try: 
        listlong <=17
    except: 
        print "Gotta be less than 17!"
        listlength()
    liststretcher()

有没有办法尝试：检查两件事，并且在移动超过异常之前要求两者都通过？或者，在继续执行liststretcher（）命令之前，我是否必须在同一个定义中创建两个不同的try：语句？

回应S.Lott，下面：我的意图是“try：listlong＆lt; = 17”将检查“listlong”变量是否小于或等于17;如果检查失败，则会转移到“除外”;如果它通过，它将转移到下面的liststretcher（）。

阅读迄今为止的答案，我有八件事需要跟进...

Answer 1

你有大部分答案：

def isIntLessThanSeventeen(listlong):
    try:
        listlong = int(listlong) # throws exception if not an int
        if listlong >= 17:
            raise ValueError
        return True
    except:
        return False

print isIntLessThanSeventeen(16) # True
print isIntLessThanSeventeen("abc") # False

Answer 2

您需要使用if语句检查关系，并在适当时手动引发异常。

Answer 3

你所缺少的，以及S.Lott试图引导你的是，listlong <= 17语句不会引发异常。它只是一个条件表达式，产生True或False，然后忽略该值。

您的意思可能是assert( listlong <= 17 )，如果条件为False则抛出AssertionError异常。

Answer 4

好吧，修复你的解决方案：

def listlength():
    print "How many things (up to 17) do you want in the list?"
    global listlong
    listlong = raw_input("> ")
    try:
        listlong = int(listlong)
        listlong <= 17
    except:
        print "Gotta be a number less than 17, chumpy!"
        listlength()
        return
    liststretcher()

问题是你在不需要时使用递归，所以试试这个：

def listlength():
    print "How many things (up to 17) do you want in the list?"
    global listlong
    listlong = raw_input("> ")
    value = None
    while value is None or and value > 17:
            try:
                listlong = int(listlong)
            except:
                print "Gotta be a number less than 17, chumpy!"
                value = None
    listlong = value
    liststretcher()

这样，该函数不会调用自身，只有在输入有效时才会调用 liststretcher 。

Answer 5

length = ""
while not length.isdigit() or int(length) > 17:
   length = raw_input("Enter the length (max 17): ")
length = int(length)

Answer 6

没有理由避免递归，这也有效：

def prompt_list_length(err=None):
    if err:
        print "ERROR: %s" % err
    print "How many things (up to 17) do you want in the list?"
    listlong = raw_input("> ")
    try:
        # See if the list can be converted to an integer,
        # Python will raise an excepton of type 'ValueError'
        # if it can't be converted.
        listlong = int(listlong)
    except ValueError:
        # Couldn't be converted to an integer.
        # Call the function recursively, include error message.
        listlong = prompt_list_length("The value provided wasn't an integer")
    except:
        # Catch any exception that isn't a ValueError... shouldn't hit this.
        # By simply telling it to 'raise', we're telling it to not handle
        # the exception and pass it along.
        raise
    if listlong > 17:
        # Again call it recursively.
        listlong = prompt_list_length("Gotta be a number less than 17, chumpy!")

    return listlong

input = prompt_list_length()
print "Final input value was: %d" % input

python初学者：在异常之前尝试两件事？

6 个答案: