What are new-style classes?

[Colin J. Williams]

Reinhold Birkenfeld wrote:
> Terry Hancock wrote:
> 
>>On Sunday 28 August 2005 04:47 am, Vaibhav wrote:
>>
>>>I recently heard about 'new-style classes'. I am very sorry if this
>>>sounds like a newbie question, but what are they? I checked the Python
>>>Manual but did not find anything conclusive. Could someone please
>>>enlighten me? Thanks!
>>
>>"New style" classes are becoming the standard in Python, and must
>>always be declared as a subclass of a new style class, including built-in
>>classes.
> 
> 
> [Warning, advanced stuff ahead!]
> 
> That's not entirely true. New-style classes need not be derived from a new-
> style class, they need to use the metaclass "type" or a derived.
> 
> So you can also declare a new-style class as
> 
> class new_class:
>     __metaclass__ = type
> 
> Or, if you want to switch a whole module with many classes to new-style, just set a
> 
> __metaclass__ = type
> 
> globally.
> 
> 
> Reinhold
What are the pros and cons of the alternate approach?

Colin W.