[Python] Why does my custom object fail to work as a dictionary key even after implementing...

I'm trying to use instances of a custom Python class as keys in a dictionary. I've overridden both __hash__() and __eq__() methods, but somehow, dictionary lookups still fail for seemingly identical keys.

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

def __eq__(self, other):
return isinstance(other, Book) and self.title == other.title and self.author == other.author

def __hash__(self):
return hash((self.title, self.author))

book1 = Book("Wings of Fire", "A.P.J. Abdul Kalam")
book2 = Book("Wings of Fire", "A.P.J. Abdul Kalam")

books_dict = {book1: "Autobiography"}

print(book2 in books_dict)


Since book1 and book2 have the same data and both __eq__ and __hash__ are defined, I expected book2 in books_dict to return True.

Continue reading...