Question

所以我正在Treehouse网站的Python课程中间，问题正是这样：

创建一个名为most_classes的函数，该函数包含教师字典。每个关键字都是教师的名字，他们的价值是他们所教授的课程清单。 most_classes应该返回班级最多的老师。

在这里，我已经在Treehouse论坛上的资源中找到了正确的代码，我已经问过同样的问题，但没有得到回复 - 那么究竟是什么分配老师=＆＃34;＆＃34;做？我很困惑

 # The dictionary will be something like:
 # {'Jason Seifer': ['Ruby Foundations', 'Ruby on Rails Forms', 'Technology Foundations'],
 #  'Kenneth Love': ['Python Basics', 'Python Collections']}

 # Often, it's a good idea to hold onto a max_count variable.
 # Update it when you find a teacher with more classes than
 # the current count. Better hold onto the teacher name somewhere
 # too!

def most_classes(my_dict):
    count = 0
    teacher = "" #this is where I am confused!
    for key in my_dict: 
        if(len(my_dict[key]) > count):
            count = len(my_dict[key])
            teacher = key   

    return teacher

Answer 1

它为教师分配默认值，将替换为代码中的实际教师姓名。

Answer 2

teacher = ""确保如果my_dict为空，则您无法在不设置teacher = key的情况下退出for循环。否则，如果my_dict为空，则会在未设置的情况下返回teacher。

如果您注释掉该行，请按以下方式调用您的函数：

most_classes({})

你会得到这个（因为teacher永远不会在返回之前被初始化）：

UnboundLocalError: local variable 'teacher' referenced before assignment

Answer 3

为什么不删除该行并对其进行测试？

def most_classes(my_dict):
    count = 0
    teacher = "" # this is where I am confused!
    for key in my_dict:
        if(len(my_dict[key]) > count):
            count = len(my_dict[key])
            teacher = key

    return teacher


def most_classes_cavalier(my_dict):
    count = 0
    for key in my_dict:
        if(len(my_dict[key]) > count):
            count = len(my_dict[key])
            teacher = key

    return teacher


if __name__ == "__main__":
    dic = {'Jason Seifer': ['Ruby Foundations', 'Ruby on Rails Forms', 'Technology Foundations'],
           'Kenneth Love': ['Python Basics', 'Python Collections']}
    print "The teacher with most classes is - " + most_classes(dic)
    print "The teacher with most classes is - " + most_classes_cavalier(dic)
    dic = {}
    print "The teacher with most classes is - " + most_classes(dic)
    print "The teacher with most classes is - " + most_classes_cavalier(dic)

这是我运行程序时得到的结果 -

The teacher with most classes is - Jason Seifer
The teacher with most classes is - Jason Seifer
The teacher with most classes is -
Traceback (most recent call last):
  File "experiment.py", line 30, in <module>
    print "The teacher with most classes is - " + most_classes_cavalier(dic)
  File "experiment.py", line 20, in most_classes_cavalier
    return teacher
UnboundLocalError: local variable 'teacher' referenced before assignment

我看到@ martijn-pieters已经提供了解释，但在这种情况下，Python解释器可以更快地为您完成。

为什么要将变量分配给＆＃34;＆＃34;？

3 个答案: