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作为一项作业，我正在尝试创建两个类：一个类 ，Book查看是否已签出一本书并返回书中的标题、作者和页码（这些是输入变量）和另一个类，称为Library，将标题-作者对添加到字典中，并查看是否已签出某些特定书籍。每次尝试运行它时，我都会收到一条错误消息。我该如何解决这个奇怪的错误？

这是我的代码：

class Book:
    def __init__(self, title, author, pages):
        self.title = title
        self.author = author
        self.pages = pages
        self.checkedOut = False

    def checked_Out(self):
        print(self.checkedOut)
        return self.checkedOut

    def change_value_of_checkedOut(self):
        if self.checkedOut == False:
            self.checkedOut = True
            print("Switched from False to True.")
        elif self.checkedOut == True:
            self.checkedOut = False
            print("Switched from True to False.")

    def return_pages(self):
        print(self.pages)
        return self.pages

    def return_title(self):
        print(self.title)
        return self.title

class Library:
    def __init__(self):
        collection = {}

    def addExistingBook(self, book):
        collection[book.title] = book.author

    def addNewBook(self, title, author, pages):
        new_book = Book(title, author, pages)
        collection[title] = new_book.author

    def change_checked_out_status(self, title):
        if title in collection.keys():
            title.change_value_of_checkedOut()
        else:
            print("This book is not in the collection.")

def main():
    title = str(input("Enter the title of the book. "))
    author = str(input("Enter the author of the book. "))
    pages = int(input("Enter the number of pages in the book. "))
    myBook = Book(title, author, pages)
    myLib = Library()
    myLib.addExistingBook(myBook)

main()

这是我尝试运行它时发生的情况：

Enter the title of the book. The Count of Monte Cristo
Enter the author of the book. Alexandre Dumas
Enter the number of pages in the book. 1250
Traceback (most recent call last):
  File "C:/Python33/Class Programs/book_library_classes.py", line 56, in <module>
    main()
  File "C:/Python33/Class Programs/book_library_classes.py", line 54, in main
    myLib.addExistingBook(myBook)
  File "C:/Python33/Class Programs/book_library_classes.py", line 36, in addExistingBook
    collection[book.title] = book.author
NameError: global name 'collection' is not defined
4

6 回答 6

2

You defined collection as a local variable in __init__:

def __init__(self):
    collection = {}

But that doesn't magically make it an instance variable. You have to do that explicitly:

class Library:
    def __init__(self):
        self.collection = {}

    def addExistingBook(self, book):
        self.collection[book.title] = book.author

Also, I wouldn't make methods like this:

def return_title(self):
    print(self.title)
    return self.title

They're just another layer of obfuscation over the straightforward book.title attribute.

Also, you don't need to write .keys(). if key in dictionary is the preferred syntax:

if title in self.collection:
于 2013-04-24T04:50:28.613 回答
1

Add self.collection where ever you are referencing collection.

于 2013-04-24T04:50:35.990 回答
1

Class members must be accessed using self.propertyName. Your code should look like this:

class Library:
    def __init__(self):
        self.collection = {}

    def addExistingBook(self, book):
        self.collection[book.title] = book.author

     ....
于 2013-04-24T04:50:56.360 回答
0

In your Collection class you have to use internal collection:

class Library:
    def __init__(self):
        self.collection = {}

    def addExistingBook(self, book):
        self.collection[book.title] = book.author

Also the last line looks suspicious. Did you mean this:

self.collection[book.title] = book
于 2013-04-24T04:51:04.537 回答
0

collection is a local variable

Try referencing it in your functions with self.collection, which should fix your problem.

于 2013-04-24T04:52:20.500 回答
0

你应该告诉 pythoncollection属于 Library 实例，myLib：

修改图书馆类说：self.collection你目前拥有的任何地方，collection 即

class Library:
    def __init__(self):
        self.collection = {}

    def addExistingBook(self, book):
        self.collection[book.title] = book.author

    def addNewBook(self, title, author, pages):
        new_book = Book(title, author, pages)
        self.collection[title] = new_book.author

    def change_checked_out_status(self, title):
        if title in self.collection.keys():
            title.change_value_of_checkedOut()
        else:
            print("This book is not in the collection.")

希望这可以帮助！

于 2013-04-24T04:55:18.283 回答