Creating new classes on the fly

[Alex Martelli]

Carlos Ribeiro <carribeiro at gmail.com> 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 found two different ways to do it in the documentation:
> 
> new.classobj(name, baseclasses, dict)

This normally makes a 'classic class', unless some baseclasses are
non-classic (e.g., object or other built-ins); note that __metaclass__
in dict is ignored.

> 
> and:
> 
> type(name, bases, dict)

This makes a new-style class (again,  __metaclass__ in dict is ignored).

> 
> I assume that both end up calling the same code, but I really don't
> know which one am I supposed to call, in terms of being the most
> 'pythonic' way. Are both the same? Is one of them preferred over the
> other?

They're not quite the same, if the bases tuple is empty or only has
classic classes.  I would normally use the second form because new-style
classes are generally preferred.


Alex