subclassing pyrex extension types in python

[greg]

Nitin wrote:

> I am trying to subclass an extension type in Python and add attributes
> to the new class but I keep getting errors.
> 
> cdef class Spam:
> 
>   cdef int amount
> 
>   def __new__(self):
>     self.amount = 0
> 
> I get an error "TypeError: 'name2' is an
> invalid keyword argument for this function"

Arguments to the constructor of a class are passed
to its __new__ method as well as its __init__ method,
so if you want to subclass it in Python, you need to
allow for that by defining it as

   def __new__(self, *args, **kwds):
     ...

Without that, your Python subclass would have to define
its own __new__ method which accepts the extra args
and strips them out, e.g.

   class MySpam(Spam):

     def __new__(cls, name1=None, name2=None):
       return Spam.__new__(cls)

--
Greg