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My code is giving the error as TypeError: __init__() takes 2 positional arguments but 4 were given. tried searching for an extra argument but couldn't get one.

Tried previously answered questions but didn't get any proper solution.

My code is as follows:

from abc import ABCMeta, abstractmethod
class Book(object, metaclass=ABCMeta):
    def __init__(self,title,author):
        self.title=title
        self.author=author   
    @abstractmethod
    def display(): pass

#Write MyBook class
class MyBook(Book):
    def __init__(self, price):
        self.price = price

    def display():
        print('Title: {}'.format(title))
        print('Author: {}'.format(author))
        print('Price: {}'.format(price))

title=input()
author=input()
price=int(input())
new_novel=MyBook(title,author,price)
new_novel.display()

compiler gives runtime error as follows

Traceback (most recent call last):
  File "Solution.py", line 23, in <module>
    new_novel=MyBook(title,author,price)
TypeError: __init__() takes 2 positional arguments but 4 were given
Vikesh Patil
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    To add to @gbtimmon, specifically, to explain the error message - `MyBook(title,author,price)` will pass four arguments: `(self, title, author, price)`. Meanwhile, `MyBook.__init__` is defined to expect only two: `(self, price)`. (What you wrote in `Book` is irrelevant.) Thus the error message ("__init__() takes 2 positional arguments but 4 were given"). – Amadan Jul 29 '19 at 17:04

2 Answers2

3

Comments inside the code. 

from abc import ABCMeta, abstractmethod


class Book(object, metaclass=ABCMeta): # 1. Why do you need meta class?
    def __init__(self, title, author):
        self.title=title
        self.author=author
    @abstractmethod
    def display(self): pass  # 2. Consider replacing with  raise NotImplementedError + missing 'self'


class MyBook(Book):
    def __init__(self, price, title, author):  # 3 You are missing two arguments in here.... (title and author)
        super(MyBook, self).__init__(title, author)  # 4 This line is missing
        self.price = price

    def display(self):
        print('Title: {}'.format(self.title))  # self missing in all three lines
        print('Author: {}'.format(self.author))
        print('Price: {}'.format(self.price))

title=input()
author=input()
price=int(input())
new_novel = MyBook(title, author, price)
new_novel.display()
Guy Tabak
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  • Actually, I was solving the problem from a competitive programming site HackerRank. The `Book()` class is already defined and it is not editable. I can just write the MyBook() class for the solution. and can't even change the parameters passed – Vikesh Patil Jul 29 '19 at 17:11
  • Alright, so implement the notes in the MyBook class - it should solve your problems. – Guy Tabak Jul 29 '19 at 17:12
  • Thank you very much for your help – Vikesh Patil Jul 29 '19 at 17:18
2

Python will not automatically call the init of the parent class. You need to do it explicitly. 

from abc import ABCMeta, abstractmethod
class Book(object, metaclass=ABCMeta):
    def __init__(self,title,author):
        self.title=title
        self.author=author   
    @abstractmethod
    def display(): pass

#Write MyBook class
class MyBook(Book):
    def __init__(self, price, title, author):
        super(MyBook, self).__init__(title, author)
        self.price = price

    def display():
        print('Title: {}'.format(title))
        print('Author: {}'.format(author))
        print('Price: {}'.format(price))
gbtimmon
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