python初学者：在异常之前尝试两件事？

我正在尝试编写一个脚本，它接受数字输入，然后检查以查看

（a） 输入实际上是一个数字，并且 （b） 该数字小于或等于17

我尝试过各种各样的“如果”语句，但都没有用，现在我正试图用“尝试”语句来表达我的想法。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()

def listlength（）：
打印“您希望列表中有多少项（最多17项）”
全球上市公司
listlong=原始输入（“>”）
尝试：
listlong=int（listlong）
listlong你得到了大部分答案：

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

您需要使用if语句来检查关系，如果合适，手动引发异常。
要修复您的解决方案：

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()

这样函数就不会调用自身，而对liststretcher的调用只会在输入有效时发生。
您缺少的，以及S.Lott试图引导您的，是语句
listlong没有理由避免递归，这也可以起作用：

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

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

，而是要具体说明要捕获哪些异常。您做了什么
listlong
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()

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

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