How can I extend a local class in a function?

How can I extend a local class in a function?

Here is the structure i'm dealing with
class myclass():
def function(self):
class localclass():
params = {'a':1, 'b': 2}
return localclass
I want to add parameters in class localclass, but not directly in class
'myclass' definition. So I want to call/override function and/or class
localclass to add params with the method
params.update({'d': 4, 'e': 5})
How do i do that?
THanks.