When I try to reuse a urllib2.Request object with different post data,
the data itself is updated, but the content length is not. Here is a
simple script to reproduce it on Python 2.5 on Fedora 10 and 2.6 on Arch
Linux:

#!/usr/bin/python
# vim: fileencoding=utf8 
# test with:  echo | socat - tcp4-listen:1111,fork
# Demonstrates bad content length of second request, which should be 2
import urllib2
req = urllib2.Request('http://localhost:1111')
req.add_data("1")
urllib2.urlopen(req)
req.add_data("10")
urllib2.urlopen(req)