為什么要為“”分配變量？

Question

所以我在Treehouse網站上的Python課程中，問的問題恰好是這樣的：

創建一個名為most_classes的函數，該函數需要一個教師詞典。 每個鍵都是老師的名字，其值是他們所教課程的列表。 most_classes應該返回班級最多的老師。

在這里，我發布了以下正確的代碼，這些代碼是我在Treehouse論壇上的資源中找到的，並且我也提出了相同的問題，但沒有得到答復-那么分配教師=“”到底有什么用？ 我感到很困惑

 # 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

它為教師分配默認值，該默認值將替換為代碼中的實際教師姓名。

Answer 2

teacher = ""確保如果my_dict為空，則在未設置teacher = key情況下不會退出for循環。 否則，如果my_dict為空，則無需設置將返回teacher 。

如果注釋掉該行，請像下面這樣調用函數：

most_classes({})

您會得到的（因為teacher在返回之前從未初始化過）：

UnboundLocalError: local variable 'teacher' referenced before assignment

Answer 3

為什么不刪除該行並對其進行測試？

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)

這是我運行程序時得到的-

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已經提供了解釋，但是在這種情況下，Python解釋器會為您更快地完成該解釋。