[python-win32] Convert RGBA to BGRA using standard library?

[Greg Ewing]

Can anyone think of an efficient way to convert a string
full of RGBA image data to BGRA, using only what's available
in the standard library?

I'm trying to add a function to PyGUI for creating an Image
object from arbitrary data. The problem I'm having is that
GDI+ on Windows expects BGRA, whereas most other platforms
deal with RGBA. I don't want to require the user to supply
the data in different formats on different platforms, so
PyGUI needs to be able to convert where necessary.

I know the conversion can be done easily using something
like PIL or numpy, but I'm after a solution that doesn't
depend on any third-party libraries.

-- 
Greg