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I'm running Windows XP.  I've been unable to find any
documentation about this exact problem - only that fwrite
thing.  But my testing shows that it works if I do
file.read(67076095), but throws an exception with
file.read(67076096).

I'm not suggesting limiting all reads from Python.  All I'm
suggesting is that under the hood the Windows implementation
of Python's read() call actually uses multiple fread() (or
whatever) calls if more than 67076095 bytes need to be read.
 That's all.  No interface changes.