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"make sense?"

So far as it goes, yes -- thanks.  At a higher level ;-),
I've been slinging Python for 15 years and have never had
any trouble with this stuff because I never push on the end
cases (I always seek when switching between reading and
writing, even if only by using the peculiar- looking
f.seek(f.tell()), and regardless of the platform du jour).

Pushing beyond that doesn't interest me.

Note that Python's file_read() (in fileobject.c) is already
much more complicated than simply calling C's fread(). 
Because of this, it may be that Python is adding strange end
case behavior beyond what the platform C would exhibit if
the latter were used directly.