[PyQt] How do I get a clean empty transparent image?

[Grzegorz Adam Hankiewicz]

I have the following lines of code:

         big = QImage(size, images[0].height(), QImage.Format_ARGB32)
         big.save("test.png")

The resulting test.png file contains random garbage, so I need to  
clean that out. I've tried to use a QPainter calling eraseRect(), but  
that removes the transparency by drawing a color. If I try setting the  
brush transparent, nothing is drawn, and nothing is cleared.

How can I clean the image leaving the image transparent?