[Cython] Argument type declaration question

[Jason Evans]

I would like to be able to write code like the following:

     cdef foo(int i, dict d, list l, str s):
	...

But somehow str is treated differently than int, dict, list, etc., which 
means I have to write:

     cdef foo(int i, dict d, list l, s):
         assert type(s) == str
         ...

I don't understand why this limitation exists.  Is it some artifact of 
the support for implicit casting for char * arguments?

Thanks,
Jason