Extending collections.defaultdict

Hi all,

I would like to create in Cython/Pyrex a new type by extending
collections.defaultdict class. I've found that I can extend dict by using :

cdef extern from "dictobject.h":
    ctypedef class __builtin__.dict [object PyDictObject]:
        pass

cdef class hdict (dict):
    ...

But there is no header file such as "dictobject.h" for module
collections nor I could find one that declares defaultdict.

Does anyone knows how I could declare the existence of defaultdict?

Thanks in advance for help.
Cheers,
Franck