pip: pip install and upgrade errors

This is the traceback when pip install twitter is given

> Downloading/unpacking twitter
Cleaning up...
Exception:
Traceback (most recent call last):
  File "/home/raj/anaconda/lib/python2.7/site-packages/pip/basecommand.py", line 122, in main
    status = self.run(options, args)
  File "/home/raj/anaconda/lib/python2.7/site-packages/pip/commands/install.py", line 278, in run
    requirement_set.prepare_files(finder, force_root_egg_info=self.bundle, bundle=self.bundle)
  File "/home/raj/anaconda/lib/python2.7/site-packages/pip/req.py", line 1177, in prepare_files
    url = finder.find_requirement(req_to_install, upgrade=self.upgrade)
  File "/home/raj/anaconda/lib/python2.7/site-packages/pip/index.py", line 194, in find_requirement
    page = self._get_page(main_index_url, req)
  File "/home/raj/anaconda/lib/python2.7/site-packages/pip/index.py", line 568, in _get_page
    session=self.session,
  File "/home/raj/anaconda/lib/python2.7/site-packages/pip/index.py", line 670, in get_page
    resp = session.get(url, headers={"Accept": "text/html"})
  File "/home/raj/anaconda/lib/python2.7/site-packages/pip/_vendor/requests/sessions.py", line 468, in get
    return self.request('GET', url, **kwargs)
  File "/home/raj/anaconda/lib/python2.7/site-packages/pip/download.py", line 237, in request
    return super(PipSession, self).request(method, url, *args, **kwargs)
  File "/home/raj/anaconda/lib/python2.7/site-packages/pip/_vendor/requests/sessions.py", line 456, in request
    resp = self.send(prep, **send_kwargs)
  File "/home/raj/anaconda/lib/python2.7/site-packages/pip/_vendor/requests/sessions.py", line 559, in send
    r = adapter.send(request, **kwargs)
  File "/home/raj/anaconda/lib/python2.7/site-packages/pip/_vendor/requests/adapters.py", line 327, in send
    timeout=timeout
  File "/home/raj/anaconda/lib/python2.7/site-packages/pip/_vendor/requests/packages/urllib3/connectionpool.py", line 488, in urlopen
    conn = self._get_conn(timeout=pool_timeout)
  File "/home/raj/anaconda/lib/python2.7/site-packages/pip/_vendor/requests/packages/urllib3/connectionpool.py", line 222, in _get_conn
    return conn or self._new_conn()
  File "/home/raj/anaconda/lib/python2.7/site-packages/pip/_vendor/requests/packages/urllib3/connectionpool.py", line 683, in _new_conn
    return self._prepare_conn(conn)
  File "/home/raj/anaconda/lib/python2.7/site-packages/pip/_vendor/requests/packages/urllib3/connectionpool.py", line 647, in _prepare_conn
    conn.connect()
  File "/home/raj/anaconda/lib/python2.7/site-packages/pip/_vendor/requests/packages/urllib3/connection.py", line 190, in connect
    ssl_version=resolved_ssl_version)
  File "/home/raj/anaconda/lib/python2.7/site-packages/pip/_vendor/requests/packages/urllib3/contrib/pyopenssl.py", line 410, in ssl_wrap_socket
    cnx.set_tlsext_host_name(server_hostname)
AttributeError: '_socketobject' object has no attribute 'set_tlsext_host_name'
Storing debug log for failure in /tmp/tmp94p6fO

Similar erri=or is raised in the case of upgrading any package. Is it a problem with pip or requests module or urllib3. Can anyone suggest a fix.