[Image-SIG] return Imaging to Python

[Fredrik Lundh]

Huiying Shen <hshen@ski.org> wrote:
> I am writing an C-extension which takes Imaging as input from Python
> interpreter as well as return Imaging back to Python environment.  I am
> having problem with the latter.  VC++5.0 says:  The instruction at
> 0x1e1388a9" referenced at "0x00000048".  The memory could not be read.
> 
> I used the identical code to generate a Python list in C and return it
> to python just fine.

an Imaging object is just an ordinary C struct,
it's not a valid Python type (it doesn't have the
PyObject_HEAD stuff required by Python).  the
Python bindings are defined in _imaging.c, and
are currently not exported to external users.

to work around this, you can:

1) link your stuff with the _imaging module,
and call PyImagingNew to wrap an Imaging
pointer in a Python-compatible Imaging-
Object (see the _imaging.c sources for
details).

or:

2) create the new image in Python code,
and pass its "id" attribute to your extension.
an example:

    def myoperation(imIn, arg):
        imIn.load()
        imOut = Image.new(imIn.mode, imIn.size, None)
        mymodule.myoperation(imIn.im.id, imOut.im.id, arg)
        return imOut

I usually use approach 2 for PIL extensions.

</F>