When I say a given instance, I mean an HTTPDigestAuthHandler object. If
I take the three lines before my loop (authhandler=, opener=,
install_opener) and move them into the loop, the problem goes away,
whereas moving only the latter two of those doesn't help. So, creating a
new HTTPDigestAuthHandler each time fixes the problem, where surely it
shouldn't make any difference? Also, I've tried sleeps of 30 seconds,
with the same results (reuse handler -> fail on the 3rd request, new
handler each time -> works for all requests).