In Python, when should I use the meta class?

Question

I went through this: What is a metaclass in Python?

But can anyone explain more specifically when to use the concept of a metaclass and when it is very convenient?

Suppose I have a class as shown below:

 class Book(object):
    CATEGORIES = ['programming','literature','physics']
    def _get_book_name(self,book):
        return book['title']
    def _get_category(self, book):
        for cat in self.CATEGORIES:
            if book['title'].find(cat) > -1:
                return cat  
        return "Other"


if __name__ == '__main__':
    b = Book()
    dummy_book = {'title':'Python Guide of Programming', 'status':'available'}
    print b._get_category(dummy_book)

For this class.

In what situation should I use the meta class and why is it useful?

Thanks in advance.

Answer 1

check out the Meta Class Made Easy link to find out how and when to use the metaclass.

Answer 2

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    def __init__(self, *args, **kwargs):
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Answer 5

If for any reason you want to do things like Class[x], x in Classetc., you need to use metaclasses:

class Meta(type):
    def __getitem__(cls, x):
        return x ** 2

    def __contains__(cls, x):
        return int(x ** (0.5)) == x ** 0.5

# Python 2.x
class Class(object):
    __metaclass__ = Meta

# Python 3.x
class Class(metaclass=Meta):
    pass

print Class[2]
print 4 in Class