The more complex example that dynamically creates a fully functional class is presented in the right pane.

As you can see, the Dog class is now equipped with two methods (feed() and bark()) and the instance attribute age.

The class name is: Dog The class is an instance of: <class 'type'> The class is based on: (<class '__main__.Animal'>,) The class attributes are: {'age': 0, 'bark': <function bark at 0x00000180C43E4E58>, '__module__': '__main__', '__doc__': None} It is feeding time! Woof, woof

output


This way of creating classes, using the type function, is substantial for Python's way of creating classes using the class instruction:

  • after the class instruction has been identified and the class body has been executed, the class = type(, , ) code is executed;
  • the type is responsible for calling the __call__ method upon class instance creation; this method calls two other methods:
    • __new__(), responsible for creating the class instance in the computer memory; this method is run before __init__();
    • __init__(), responsible for object initialization.

Metaclasses usually implement these two methods (__init__, __new__), taking control of the procedure of creating and initializing a new class instance. Classes receive a new layer of logic.


Code

def bark(self):
print('Woof, woof')

class Animal:
def feed(self):
print('It is feeding time!')

Dog = type('Dog', (Animal, ), {'age':0, 'bark':bark})

print('The class name is:', Dog.__name__)
print('The class is an instance of:', Dog.__class__)
print('The class is based on:', Dog.__bases__)
print('The class attributes are:', Dog.__dict__)

doggy = Dog()
doggy.feed()
doggy.bark()
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