Certbot-auto fails on debian wheezy, hangs on "Installing Python packages..."

The problem has nothing to do with Debian Wheezy. I’m running Debian Jessie (Debian 8.10) and I get the same result. Before running certbot-auto I did apt-get update and apt-get upgrade to make sure my Jessie installation is up-to-date.
When I (as root) type: certbot-auto
the messages are slightly different from debianuser’s reflecting the fact that I’m using jessie not wheezy, but it hangs in exactly the same way, after “Installing Python packages…”, and when I kill it with ctrl-C the traceback starts with exactly the same lines in the same modules.
Installing Python packages…
^CTraceback (most recent call last):
File “/tmp/tmp.YumJ6Yaqo1/pipstrap.py”, line 184, in
exit(main())
File “/tmp/tmp.YumJ6Yaqo1/pipstrap.py”, line 165, in main
for path, digest in PACKAGES]
File “/tmp/tmp.YumJ6Yaqo1/pipstrap.py”, line 120, in hashed_download
response = opener(using_https=parsed_url.scheme == ‘https’).open(url)
File “/usr/lib/python2.7/urllib2.py”, line 437, in open
response = meth(req, response)
File “/usr/lib/python2.7/urllib2.py”, line 550, in http_response
‘http’, request, response, code, msg, hdrs)
File “/usr/lib/python2.7/urllib2.py”, line 469, in error
result = self._call_chain(*args)
File “/usr/lib/python2.7/urllib2.py”, line 409, in _call_chain
result = func(*args)
File “/usr/lib/python2.7/urllib2.py”, line 656, in http_error_302
return self.parent.open(new, timeout=req.timeout)
File “/usr/lib/python2.7/urllib2.py”, line 431, in open
response = self._open(req, data)
File “/usr/lib/python2.7/urllib2.py”, line 449, in _open
‘_open’, req)
File “/usr/lib/python2.7/urllib2.py”, line 409, in _call_chain
result = func(*args)
File “/usr/lib/python2.7/urllib2.py”, line 1240, in https_open
context=self._context)
File “/usr/lib/python2.7/urllib2.py”, line 1194, in do_open
h.request(req.get_method(), req.get_selector(), req.data, headers)
File “/usr/lib/python2.7/httplib.py”, line 1039, in request
self._send_request(method, url, body, headers)
File “/usr/lib/python2.7/httplib.py”, line 1073, in _send_request
self.endheaders(body)
File “/usr/lib/python2.7/httplib.py”, line 1035, in endheaders
self._send_output(message_body)
File “/usr/lib/python2.7/httplib.py”, line 879, in _send_output
self.send(msg)
File “/usr/lib/python2.7/httplib.py”, line 841, in send
self.connect()
File “/usr/lib/python2.7/httplib.py”, line 1242, in connect
HTTPConnection.connect(self)
File “/usr/lib/python2.7/httplib.py”, line 822, in connect
self.timeout, self.source_address)
File “/usr/lib/python2.7/socket.py”, line 562, in create_connection
sock.connect(sa)
File “/usr/lib/python2.7/socket.py”, line 224, in meth
return getattr(self._sock,name)(*args)
KeyboardInterrupt

Failure in precisely the same way on different Debian versions suggests that some recent change to certbot-auto has introduced a bug.