21st December 2005, 1 min read

Metaclass programming in Python

I’m a few years behind, but while I knew you could modify classes in Python, it turns out you can do it conveniently as of Python 2.2.

Here’s how you can dynamically create a class:
>>> from new import classobj


Foo2 = classobj('Foo2',(),{"mymethod":lambda self,x: x})
Foo2().mymethod(2)
2


Once the class has been created, you can easily modify it as well:

>>> setattr(Foo2,'anothermethod',lambda self,x: 2*x)


Foo2().anothermethod(2)
4


I recall that I found ways to achieve the same result by manipulating directly class objects, but this is much neater.

You can even dynamically change the class of an object:
>>> t.class=classobj('newFoo2', (Foo2,), {"supermethod":lambda self,x: 5*x})


t.supermethod(2)
10


That’s pretty satisfying.