Description of problem:
See e.g. http://permalink.gmane.org/gmane.comp.python.enthought.devel/27376

This appears to be a regression in python 2.6.6 relative to 2.6.5

Upstream bug report:
  http://bugs.python.org/issue9639

It is fixed in the upstream 2.7 branch, but was not backported to 2.6 as it's not a security fix:
  http://svn.python.org/view?view=rev&revision=84207


Version-Release number of selected component (if applicable):
  python-2.6.6-3.el6.x86_64

How reproducible:
  100%


Steps to Reproduce:
  Run the following python code fragment, from the enthought mailing list (which relies on browserspy.dk):

---- BEGIN QUOTE ----
import urllib2

passman = urllib2.HTTPPasswordMgrWithDefaultRealm()
passman.add_password(None, 'http://browserspy.dk', 'test', 'test')
authhandler = urllib2.HTTPBasicAuthHandler(passman)
opener = urllib2.build_opener(authhandler)

for i in xrange(10):
    print "Loop {0}".format(i)
    pagehandle = opener.open('http://browserspy.dk/password-ok.php')
    pagehandle.close()
---- END QUOTE -----


Actual results:
  With 2.6.6, it fails on i == 6 with this output:

---- BEGIN QUOTE ----
Loop 0
Loop 1
Loop 2
Loop 3
Loop 4
Loop 5
Loop 6
Traceback (most recent call last):
  File "<stdin>", line 3, in <module>
  File "/usr/lib64/python2.6/urllib2.py", line 397, in open
    response = meth(req, response)
  File "/usr/lib64/python2.6/urllib2.py", line 510, in http_response
    'http', request, response, code, msg, hdrs)
  File "/usr/lib64/python2.6/urllib2.py", line 429, in error
    result = self._call_chain(*args)
  File "/usr/lib64/python2.6/urllib2.py", line 369, in _call_chain
    result = func(*args)
  File "/usr/lib64/python2.6/urllib2.py", line 864, in http_error_401
    url, req, headers)
  File "/usr/lib64/python2.6/urllib2.py", line 833, in http_error_auth_reqed
    headers, None)
urllib2.HTTPError: HTTP Error 401: basic auth failed
---- END QUOTE -----


Expected results:
With python-2.6.5-9.fc14.x86_64, it successfully runs 10 iterations:
---- BEGIN QUOTE ----
Loop 0
Loop 1
Loop 2
Loop 3
Loop 4
Loop 5
Loop 6
Loop 7
Loop 8
Loop 9
---- END QUOTE -----


(See also bug 649274)