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Python Object-Oriented Python Advanced Objects Constructicons

Henry Lin
Henry Lin
11,636 Points
Posted by Henry Lin
Henry Lin
11,636 Points

The difference between str(bc.books) and str(bc.books[0])?

In the class of Book of books.py, Kenneth overrode the str function which would return a books info. However, when I tried to look up both books' info in books, it returned information about memory instead of the string representation of books.

Here is my understanding so far:

In the Bookcase class, the @classmethod create_bookcase() returns an instance of Bookcase, and during the process, it also extracts info from book_list and passes it to Book class so that every time the for loop executes, it creates a Book instance and stored it in books[] list. Therefore, by the time the code gets executed completely, there is a Bookcase instance, and two Book instances(based on the video).

Thus, when we type bc, the console would show the object info of Bookcase. When we use the overrode method str(bc.books), I thought it would have returned the two books "real info" (title, author) because bc.books invoked the attributes in Book class. Hence, str in Book class should take place.

But it's not the case !! Can someone explain this question?

1 Answer

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,457 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,457 Points

Great question! Let's look at each case

str(bc) --> Since bc has no __str__, so it reports out the object information

str(bc.books) --> bc.books is a list that has a built-in __str__ method. However, this __str__ method has the default behavior of calling __repr__ on each of the items in the list. So, only the object information is shown. More in the docs.

str(bc.books[0]) --> bc.books[0] is a reference to a Book object that has it's own __str__ method so the output is "title by author"

Post back if you have more questions. Good Luck!!

Henry Lin
Henry Lin
11,636 Points
Henry Lin
Henry Lin
11,636 Points

Thank you so much! I got it now.