python - 使用 Get 访问字典

Question

For this problem assume the following assignment statement has been executed.

weekdays = {'Sunday':0, 'Monday':1, 'Tuesday':2, 'Wednesday':3,
            'Thursday':4, 'Friday':5, 'Saturday':6}

Assume the variable day contains a value that may or may not be the name of a day. Write an assignment statement using get that assigns to day_num the day number if day contains the name of a day and -1 otherwise.

For example, if day is 'Wednesday' then day_num should be 3 and if day is 'Talk Like a Pirate Day' then day_num should be -1.

这是我的代码:

day_num = weekdays.get(day)
if day_num==None:
   day_num=-1

我就是不明白为什么还是错误；我认为这是正确的。作业系统不断显示

You should use only one assignment statement (and nothing else)

Answer 1

您正在使用两个赋值语句。也许你应该给dict.get() 第二个参数:

day_num = weekdays.get(day, -1)

如果字典中不存在day，则默认返回第二个参数；默认值是 None，但这里我返回 -1。

这可以为您节省一次 is None 测试和第二次作业。