Valid for newest selenium and pep8 compliant.

PersistentWebdriver.py

from selenium import webdriver

from selenium.webdriver.remote.remote_connection import RemoteConnection
from selenium.webdriver.remote.errorhandler import ErrorHandler


class PersistentWebdriver (webdriver.Remote):

    def __init__(self, command_executor='http://127.0.0.1:4444/wd/hub',
        desired_capabilities=None, browser_profile=None, proxy=None,
        session_id=None, browser_name=''):

        platform = version = ''
        javascript_enabled = True

        self.command_executor = command_executor
        if type(self.command_executor) is str:
            self.command_executor = RemoteConnection(command_executor)

        self.command_executor._commands['GET_SESSION'] = \
            ('GET', '/session/$sessionId')

        self.session_id = session_id
        self.capabilities = {}
        self.error_handler = ErrorHandler()

        if session_id:
            self.connect_to_session(
                browser_name=browser_name,
                platform=platform,
                version=version,
                javascript_enabled=javascript_enabled
            )
        else:
            self.start_session(
                desired_capabilities=desired_capabilities,
                browser_profile=browser_profile
            )

    def connect_to_session(self, browser_name, platform, version,
                           javascript_enabled):

        response = self.execute('GET_SESSION', {
            'desiredCapabilities': {
                'browserName': browser_name,
                'platform': platform or 'ANY',
                'version': version or '',
                'javascriptEnabled': javascript_enabled
            },
            'sessionId': self.session_id
        })
        self.session_id = response['sessionId']
        self.capabilities = response['value']