“NoneType”对象在“24小时内自学Python”的第9章中没有属性'__getitem__‘

Question

我正在用2.7.6来完成这本书，我得到了一个错误。我已经逐行检查过，以确保没有任何排字。我(显然)对Python还不太了解，甚至不知道从哪里开始。如果能帮上忙我会很感激的。

以下是代码：

def get_specials():
        monday = {'B': 'Horseradish omelet. Note: Better than it sounds.',
                  'L': 'Momma\'s Curry.  Note: Can be made spicy.',
                  'D': 'Beef brisket.  Note:Comes with au jus. That\'s pronounced "Oh jhoo", not "Ow Juice."'}

        tuesday = {'B': 'Sausage gravy over biscuits. Note: Toast can be subbed.',
                   'L': 'Grilled cheese and tomato soup. Note: We have vegan cheese.',
                   'D': 'Meatloaf. Note: Comes with catsup on the top. Not optional.'}

        wednesday = {'B': 'Horseradish omelet. Note: Better than it sounds.',
                  'L': 'Momma\'s Curry.  Note: Can be made spicy.',
                  'D': 'Beef brisket.  Note:Comes with au jus. That\'s pronounced "Oh jhoo", not "Ow Juice."'}

        thursday = {'B': 'Sausage gravy over biscuits. Note: Toast can be subbed.',
                   'L': 'Grilled cheese and tomato soup. Note: We have vegan cheese.',
                   'D': 'Meatloaf. Note: Comes with catsup on the top. Not optional.'}

        friday = {'B': 'Horseradish omelet. Note: Better than it sounds.',
                  'L': 'Momma\'s Curry.  Note: Can be made spicy.',
                  'D': 'Beef brisket.  Note:Comes with au jus. That\'s pronounced "Oh jhoo", not "Ow Juice."'}

        saturday = {'B': 'Sausage gravy over biscuits. Note: Toast can be subbed.',
                   'L': 'Grilled cheese and tomato soup. Note: We have vegan cheese.',
                   'D': 'Meatloaf. Note: Comes with catsup on the top. Not optional.'}

        sunday = {'B': 'Horseradish omelet. Note: Better than it sounds.',
                  'L': 'Momma\'s Curry.  Note: Can be made spicy.',
                  'D': 'Beef brisket.  Note:Comes with au jus. That\'s pronounced "Oh jhoo", not "Ow Juice."'}

        specials = {'M': monday,
                    'T': tuesday,
                    'W': wednesday,
                    'R': thursday,
                    'F': friday,
                    'St': saturday,
                    'Sn': sunday}

def print_special(special):
        print "The special is:"
        print special
        print "*"*15

def get_day():
        while True:
                day = raw_input("Day (M/T/W/R/F/St/Sn): ")
                if day.upper() in ['M', 'T', 'W', 'R', 'F', 'ST', 'SN']:
                        return day.upper()
                else:
                        print "I'm sorry, but {} isn't valid.".format(day)

def get_time():
        while True:
                time = raw_input("Time (B/L/D): ")
                if time.upper() in ['B', 'L', 'D']:
                        return time.upper()
                else:
                        print "I'm sorry, but {} isn't a valid time.".format(time)

def main():
        specials = get_specials()
        print "This script will tell you the specials for any day of the week, and any time."
        while True:
                day = get_day()
                special = specials[day]
                time = get_time()
                print_special(special[time])
                another = raw_input("Do you want to check another day and time? (Y/N")
                if another.lower() == 'n':
                        break

if __name__ == '__main__':
        main()

而错误是：

Traceback (most recent call last):
  File "C:/Users/User/Desktop/Python/9.py", line 71, in <module>
    main()
  File "C:/Users/User/Desktop/Python/9.py", line 64, in main
    special = specials[day]
TypeError: 'NoneType' object has no attribute '__getitem__'

Answer 1

get_specials函数应该在结束时返回specials字典：

def get_specials():
    # …

    specials = {'M': monday,
                'T': tuesday,
                'W': wednesday,
                'R': thursday,
                'F': friday,
                'St': saturday,
                'Sn': sunday}
    return specials

这样，当你做specials = get_specials()时，你实际上得到了那本字典的内容。如果没有，那么调用get_specials()将返回None (即不包含任何信息)，这当然不包含任何信息。

Answer 2

您的问题是，get_specials()没有返回语句。因为它没有返回任何东西，所以行

specials = get_specials()

将specials赋值为None，因此specials[day]试图在None中查找索引，该索引由于您看到的错误而失败。