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Bug/feature request 1260171 addresses the same basic issue,
but with the idea of a method like Popen.communicate() that
writes and reads directly to/from file-like objects, instead
of reading and returning strings.
http://sourceforge.net/tracker/index.php?func=detail&aid=1260171&group_id=5470&atid=105470

But having submitted that other request, I have no real
opinion of one technique over the other, except that one of
them would be really nice to have.