[Pyrex] cdef'd classes initialization

[Lenard Lindstrom]

On 8 Aug 2006 at 18:33, Daniele Varrazzo wrote:

> Hello,
> 
> i wrote some Pyrex classes to wrap C structures. Usually such classes
> are responsible for the wrapped structure, and properly allocate them on
> the heap and initialize on __init__ and free on __dealloc__. This is the
> normal behaviour for all the instances directly created by a Python program.
> 
First, it is better to use __new__ instead of __init__ for C members.

> Inside Pyrex, i don't always want such behavior. For example i have some
> composite structures: the component is accessed from the composing
> structure using a property. When the property __get__ is invoked, i
> create from Pyrex a new instance to wrap the component structure. But
> this instance doesn't own the wrapped structure: on __dealloc__ it must
> not free() anything.
> 
You can use a root class for the case of no allocation/deallocation, 
and a derived class to export to Python. Here is an example. It also 
shows how to access C members/methods from a factory function.

cdef class CRoot:
    """For factory function"""
    cdef int datum

    def get_datum(self):
        return self.datum

def make_object(int datum):
    cdef CRoot o
    o = CRoot()
    o.datum = datum
    return o

cdef class C(CRoot):
    """Has allocator/deallocator"""
    def __new__(self, int datum):
        self.datum = datum

    def __dealloc__(self):
        pass

Lenard Lindstrom
<len-l at telus.net>