[chirp_devel] python2/3 MemoryMap?

I'm trying to write a driver that works with both Python 2 and Python 3. It works and passes all tests, but it cannot create a memory savable memory map when it downloads from the radio. I can choose MemoryMapBytes, which works in Py3, or MemoryMap, which is implemented in both but which results in a mmap that cannot be written to a file. I'm now officially lost, which is my usual state. Any suggestions?