Question

我是蟒蛇新手并从Udacity学习语言。我想写一个python程序，它占用2个日期并输出这两个日期之间的日差，假设第二个日期是后者。

它抛出错误说：

File /Users/gonewiththewind/Documents/days old.py", line 20, in daysBetweenDates
    currentDaysOfMonths = daysOfMonths[isLeap(year)][month - 1]
TypeError: list indices must be integers, not NoneType"
when I tried to call the function by "daysBetweenDates(1995,7,28,2018,1,26)

以下是代码：

daysOfMonths = [[31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31], [31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]]


def isLeap(year):
    if year % 400 == 0:
        return True
    else:
        if year % 100 == 0:
            return False
        else:
            if year % 4 == 0:
                return True

def daysBetweenDates(year1, month1, day1, year2, month2, day2):
    counter = 0
    month = month1
    year = year1
    day = day1
    while(year != year2 or month != month2 or day != day2):
        currentDaysOfMonths = daysOfMonths[isLeap(year)][month - 1]

        if(day < currentDaysOfMonths):
            day = day + 1
            counter = counter + 1
            print 'counter = '+ counter
        else:
            day = 1
            if(month1 < 12):
                month = month + 1
            else:
                month = 1
                year = year + 1
            counter = counter + 1
            print 'counter = '+ counter

    return counter

Answer 1

return函数中缺少is_leap：

def isLeap(year):
    if year % 400 == 0:
        return True
    else:
        if year % 100 == 0:
            return False
        else:
            if year % 4 == 0:
                return True
            else:
                return False  # <-- here!

否则，此函数将在该位置隐式返回None，这是非真实的，但不是bool，因此不是int（bool是int的子类，它可以使0-1-index魔法成为可能，可以用作list索引。顺便说一句，如果else块中有return，则不需要if：

def isLeap(year):
    if not year % 400:
        return True
    if not year % 100:
        return False
    # return not year % 4  # is also possible here
    if not year % 4:
        return True
    return False  # <-- needed to avoid None being returned

这是否更具可读性取决于具体情况。但是在这里，有多个嵌套分支，我认为它有助于保持较低的缩进水平并了解正在发生的事情。

python错误“列表索引必须是整数而不是非类型”

1 个答案: