Stefan, thanks for the patch.  The problem is that on FreeBSD and Solaris, if the command fails, I/O redirection does not create the file, whereas on Linux and OS X it does.  So I was going to wrap the os.remove() of the temp file in a try/except.  But I like your patch better because it avoids the dpkg-architecture call in the first place on systems that don't have it, albeit at the cost of traversing $PATH.