[Python] In Python, when should I use a meta class?

I have gone through this: What is a metaclass in Python?

But can any one explain more specifically when should I use the meta class concept and when it's very handy?

Suppose I have a class like 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 which situation should I use a meta class and why is it useful?

Thanks in advance.

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