Dynamic type creation in python

Long long time ago, in a galaxy far far away, before python 2.2+ was invented, classes and types were very different. Finally an update came and unified them. Nowadays those statements mean pretty much the same (python 2.7 / 3.X), so by stating "dynamic type creation" we actually mean "dynamic class creation" (not the other way round - this way it looks more OOP). There is a magic keyword type, which returns a type(class) of an object.

>>> class Test(object):
...     pass
...
>>> inst = Test()
>>> type(inst)
<class '__main__.Test'>




This seams logic, however the type function may be also used for dynamic class creation. We have to provide a new class name, a list of base classes and some additional attributes. For example we want to create a new class that extends Test.

>>> Test2 = type("Test2", (Test,), {"my_func" : lambda self: "Hello"})
>>> Test2
<class '__main__.Test2'>
>>> Test2.__dict__
dict_proxy({'my_func': <function <lambda> at 0x12126e0>, '__module__': '__main__', '__doc__': None})
>>> inst2 = Test2()
>>> inst2.my_func()
'Hello'

This mechanism may not be so spectacular before you apply it with a sophisticated library/framework, tomorrow I'll present how to use it with django forms.

Cheers!

KR