Creating new classes on the fly

Troy Melhase troy.melhase at
Tue Oct 5 23:04:39 CEST 2004

On Tue, 5 Oct 2004 17:53:35 -0300, Carlos Ribeiro <carribeiro at> wrote:
> I need to create new classes on the fly with different default
> parameters, stored as class attributes. Of course, there's a reason
> behind it: I need new classes, because I need to be able to build
> multiple instances of them later. And I need new defaults, because the
> values can't be provided at instantiation time (because of scoping &
> mutability issues).

I've had the same need recently, and I've found that coding the class
as part of a closure is readable (untested code):

def my_custom_class():
    some_param = lookup_param() # now part of the lexical scope, can be mutable

    class MyCustomClass:
        default_param = some_param

    return MyCustomClass

CustomizedClass1 = my_custom_class()
CustomizedClass2 = my_custom_class()

instances_of_one = [CustomizedClass1(), CustomizedClass1(), ]
instances_of_two = [CustomizedClass2(), CustomizedClass2(), ]

Good luck,

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