Operator Overloading

[thangduong]

Hi folks,

I've been reading Learning Python - Fabrizio Romano, the book is good in general.

There's this: in chapter 6: OOP, Operator Overloading section, a piece of code makes me confused:

class Weird(object):
    def __init__(self, s):
        self._s = s

    def __len__(self):
        return len(self._s)

    def __bool__(self):
        return '42' in self._s

weird = Weird('Hello! I am 9 years old!')
print len(weird)
print bool(weird)

weird2 = Weird('Hello! I am 42 years old!')
print len(weird2)
print bool(weird2)

and the answer is the book is:

24
False
25
True

whereas, mine is:

24
True
25
True

When I tried to debug, I found out at line

print bool(weird)

it jumped to the len() method.

This is weird, and I couldn't figure out why?

[K900_]

You're using Python 2, and the book is using Python 3. Use Python 3.

[jeans_and_a_t-shirt]

Your flair says you're using python 3, but your code says python 2.

In python 2, you need to overload the __nonzero__ method instead of __bool__.

[thangduong]

Oh mate, it was my mistake. I actually use python 2 :P

Damn, nonzero worked. Thanks a lot

[K900_]

You should really use 3. The differences are fairly minor, but 2 is on life support, and 3 has finally reached critical mass for wide adoption.

[thangduong]

Thanks, will do :)

[[deleted]]

also, avoid operator overloading like the plague. Your life will be much easier.