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Mastering Object-oriented Python by Steven Lott

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The __new__() method and metaclasses

The other use case for the __new__() method as a part of a metaclass is to control how a class definition is built. This is distinct from how __new__() controls building an immutable object, shown previously.

A metaclass builds a class. Once a class object has been built, the class object is used to build instances. The metaclass of all class definitions is type. The type() function is used to create class objects.

Additionally, the type() function can be used as a function to reveal the class of an object.

The following is a silly example of building a new, nearly useless class directly with type() as a constructor:

Useless= type("Useless",(),{})

Once we've created this class, we can create objects of this Useless ...

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