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It might be a very simple question but I am very confused with where I am going right now. Here is a very basic class:

class Book(object):
    def __init__(self, title, price):
        self.book = {'title':title, 'price':price}
And when I run this:
book = Book('foo', 300)
book['price']
It spits out:
TypeError: 'Book' object has no attribute '__getitem__'
I know that it's not the conventional way of initializing an instance since I am using a dictionary. But I wonder why that code is spitting out a TypeError. How do I go about solving this issue?
Thank you in advance.
ps. The book instance's type is class?
It's because a class is not a dict object.
Accessing properties on a instance of a class is done via the dot operator.
book.book['price'] 
If you want to access keys within your dict directly on your class instance you would have to implement the __getitem__ method on your class.
def __getitem__(self, key):
    return self.book[key]
book['price']
Yes. book is an object of class Book because you initialized it that way.
book = Book('foo', 300)
book['price']
print book.book['price']
So you want to access a dictionary called book of an object referenced as book and you want to extract the value of price from the dictionary. 
Usually [] operator looks for __getitem__() method and passes the requested key as an argument. Łukasz R. has shown how to do that. Dictionaries perform a key lookup while arrays find the slice or index. 
It is explained in details here : https://docs.python.org/2/reference/datamodel.html
Now because you're creating a class here, why do you want to create a separate dictionary for native must-have attributes of the class. Create attributes like the following example:
class Book(object):
    def __init__(self, title, price):
        self.title = 'foo'
        self.price = 300
book = Book('foo', 300)
print book.title
book.book['price'] would work.
For accessing proxy member you'll have to implement __getitem__ magic method.
class Book(object):
    def __init__(self, title, price):
        self.book = {'title':title, 'price':price}
    def __getitem__(self, item):
        return self.book[item]
class Book(object):
    def __init__(self, title, price):
        self.book = {'title':title, 'price':price}              
book = Book('foo', 300)
print book.book['price']
        
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