README.md

Index

1. classes are objects too
2. how to create a simple metaclass
3. using namespace in metaclasses
4. an awesome example using metaclass
5. how to use metaclasses to create singleton classes in python
6. how django rest framework uses metaclasses
7. how django uses metaclasses to maintain backward compatability

an awesome example using metaclass

Most people must be familiar with the json.dumps function.

>>> import json
>>> json.dumps({'one':1})
'{"one": 1}'
>>> 

As per the documentation json.dumps takes as parameter the value it has to dump. Now, what I can achieve with metaclass is I can introduce dumps method into my own class.

>>> class _D(type):
...     def __init__(cls, name, bases, dict):
...         from json import dumps 
...         super(_D, cls).__init__(name, bases, dict)
...         setattr(cls, 'dumps', dumps)

>>> class A(dict, metaclass=_D):
...  pass
>>> a = A()
>>> a.__setitem__('one', 1)
>>> a.dumps()
'{"one": 1}'
>>> 

In the above function when dumps is attached to the class, the function becomes a method with first parameter as self. So, similarily I can attach the print function and whatever function I wish to. I can import some function from somewhere and just attach it to my class. If you are making a library this approach will allow your user to not care about the definition of the method.