python doubly linked list class

Question

so i have two classes - one is a book library that is implemented as a doubly linked list and the other class is a DLL node class for a book node which is this:

class Book:
def __init__(self,name,author,dateadded,viewed = False, nextnode=None, prevnode=None):
    self._name = name
    self._author = author
    self._dateadded = dateadded
    self._viewed = viewed
    self._next = nextnode
    self._prev = prevnode

def __str__(self):
    """ Return string representation of book """
    outstr = ""
    outstr += self._name + " /n"
    outstr += self._author + "/n"
    outstr += self._dateadded
    return outstr

def read(self):
    """ Simulates the book being read & return string representation of the book """
    self._viewed = True
    outstr = "CURRENTLY READING: "
    outstr += self._name
    return outstr

my book library class which deals with a sequence of the book nodes, looks like this:

class BookLibrary:

""" A Doubly Linked List implementing a book library """

def __init__(self):
    self.size = 0
    self.head = None
    self.tail = None

the problem im having is within my add_book() method - when i run it the error im getting is TypeError: add_book() takes 1 positional argument but 5 were given . This is the function itself, I dont really know where im going wrong :(

def add_book(book):
    """ Add a book to the library in decreasing order of dateadded """
    n = Book(book)
    if self.size == 0:
        self.head = n
        self.tail = n
        current_book = n
        self.size += 1

    elif self.head._dateadded <= n._dateadded:
        n._next = self.head
        self.head._prev = n
        n._prev = None
        self.head = n
        self.size += 1

    elif self.tail._dateadded <= n._dateadded:
        self.tail._prev._next = n
        n._prev = self.tail._prev
        n._next = self.tail
        self.tail._prev = n
        self.size += 1

    elif self.size != 0:
        iterator = self.head._next
        while iterator._next is not None:
            if n._dateadded >= iterator._dateadded:
                n._prev = iterator._prev
                iterator._prev._next = n
                n._next = iterator
                iterator._prev = n
                self.size += 1
                break
            else:
                iterator = iterator._next
    return None

i would really appreciate any help thank you

this is the code i run:

book_lib = BookLibrary()
book_lib.add_book("Harry Potter", "JK ROWLING", 19990101, False)

0TTT0 · Accepted Answer · 2017-10-21 00:12:13Z

2

If you are passing in all of the arguments to add_book() that you would to the class Book, this is your problem. It is only expecting one argument, book, but I assume you are passing in all of the arguments that class Book expects.

You are better off instantiating your book objects first and then passing them directly into your add_book method.

answered Oct 21, 2017 at 0:12

0TTT0

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4 Comments

DecafOyster208 Over a year ago

i see what you're saying but is not instantiating the book object in the line : n = Book(book) in the add_book() method already

0TTT0 Over a year ago

no you need to instantiate it in your main code , ideally you would create a book and than add it to the Library. but if you want to add it dynamically you can do book_lib.add_book(Book("Harry Potter", "JK ROWLING", 19990101, False))

0TTT0 Over a year ago

also, if you want your code to run you are going to have to add self as the first parameter to add_book def add_book(self, book):

0TTT0 Over a year ago

and the last thing you need to do is change all of your ns in the add_book function to book

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