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paul_g's option #1 is the only that takes no work, so is the
only one I'm volunteering for <0.5 wink>.  Docs would be
good.  #4 is in general impossible short of Python
implementing its own I/O -- "the last" operation done on a C
stream isn't necessarily visible to the Python
implementation (extensions can and do perform their own I/O
on C streams directly via platform C stdio calls -- Python
has no way to know about that now even in theory).

BTW, I don't understand:

"""1. in the f.read()+f.write()+f.read() case, the f.write()
generates an IOError. this deviates from ansi c, but is in
line with msdn docs."""

All behavior in that case is explicitly not defined by ANSI
C if there isn't a file-positioning operation too between
the read() and write(), and again between the write() and
read().  Raising an exception is fine by ANSI C in that
case.  So is a segfault.  So is reading nothing, or reading
a terabtye, or wiping the disk clean, etc:  nothing is
defined about it.