Problem with psd and Alpha

Hi, i'm tryng to composite several psd coming from my render software.
Each one is a psd with  the same size of the others and an alpha  
channel.
The problem is when i do

im = Image.open("filepath")

I alway get a "RGB" image instead of "RGBA" so i can't use the alpha  
channel as mask when i compose the image.

Here some snippet:

 >>> im = Image.open("prova0000.psd")
 >>> im.mode
'RGB'
 >>> im.split()
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
   File "/Library/Python/2.5/site-packages/PIL/Image.py", line 1497,  
in split
     if self.im.bands == 1:
AttributeError: 'NoneType' object has no attribute 'bands'
 >>> repr(im.im)
'None'
 >>> im.load()
<PixelAccess object at 0x52160>
 >>> repr(im.im)
'<ImagingCore object at 0x520f0>'
 >>> im.split()
(<Image.Image image mode=L size=146x90 at 0x42C7B0>, <Image.Image  
image mode=L size=146x90 at 0x42C828>, <Image.Image image mode=L  
size=146x90 at 0x42C940>)

Thanks,
Martino.
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