On Python 2.7.9, if I set an https_proxy environment variable, where the password contains a '/' character, urllib2 fails. Given this test code:

  import os, urllib
  os.environ['http_proxy'] = "http://someuser:a/b@10.11.12.13:1234"
  f = urllib.urlopen('http://www.python.org')
  data = f.read()
  print data

I expect this error message (because my sample proxy is totally bogus):

[areitz@SOMEHOST ~]$ python2.7 test.py
Traceback (most recent call last):
  File "test.py", line 3, in <module>
    f = urllib.urlopen('http://www.python.org')
  File "/usr/lib64/python2.7/urllib.py", line 87, in urlopen
    return opener.open(url)
  File "/usr/lib64/python2.7/urllib.py", line 213, in open
    return getattr(self, name)(url)
  File "/usr/lib64/python2.7/urllib.py", line 350, in open_http
    h.endheaders(data)
  File "/usr/lib64/python2.7/httplib.py", line 997, in endheaders
    self._send_output(message_body)
  File "/usr/lib64/python2.7/httplib.py", line 850, in _send_output
    self.send(msg)
  File "/usr/lib64/python2.7/httplib.py", line 812, in send
    self.connect()
  File "/usr/lib64/python2.7/httplib.py", line 793, in connect
    self.timeout, self.source_address)
  File "/usr/lib64/python2.7/socket.py", line 571, in create_connection
    raise err
IOError: [Errno socket error] [Errno 101] Network is unreachable

Instead, I receive this error:

[areitz@SOMEHOST ~]$ python2.7 test.py
Traceback (most recent call last):
  File "test.py", line 3, in <module>
    f = urllib.urlopen('http://www.python.org')
  File "/usr/lib64/python2.7/urllib.py", line 87, in urlopen
    return opener.open(url)
  File "/usr/lib64/python2.7/urllib.py", line 213, in open
    return getattr(self, name)(url)
  File "/usr/lib64/python2.7/urllib.py", line 339, in open_http
    h = httplib.HTTP(host)
  File "/usr/lib64/python2.7/httplib.py", line 1107, in __init__
    self._setup(self._connection_class(host, port, strict))
  File "/usr/lib64/python2.7/httplib.py", line 712, in __init__
    (self.host, self.port) = self._get_hostport(host, port)
  File "/usr/lib64/python2.7/httplib.py", line 754, in _get_hostport
    raise InvalidURL("nonnumeric port: '%s'" % host[i+1:])
httplib.InvalidURL: nonnumeric port: 'a'

Note that from the error, it seems as if urllib2 is incorrectly parsing the password from the proxy URL. When trying this with curl 7.19.7, I see the proper behavior (the correct password is parsed from the proxy URL).