AttributeError: 'bytes' object has no attribute 'data'

the purpose of this script is to use python to login on a website with login and pass

launching the script with login and pass as parameters.

[vegasus@Ph3NyX:~]$python3 grabbit.py mylogin mypass

Traceback (most recent call last):
  File "/Users/vegasus/PycharmProjects/Lesson_Python/grabbit.py", line 102, in <module>
    WebLogin('mylogin', 'mypass')
  File "/Users/vegasus/PycharmProjects/Lesson_Python/grabbit.py", line 61, in __init__
    response = self.login()
  File "/Users/vegasus/PycharmProjects/Lesson_Python/grabbit.py", line 82, in login
    response = self.opener.open(login_url.encode(), login_data.encode())
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/urllib/request.py", line 444, in open
    req.data = data
AttributeError: 'bytes' object has no attribute 'data'

here is the script :

import urllib, urllib.request, urllib.parse
import http.cookiejar
import sys

class WebLogin(object):

    def __init__(self, username, password):

        # url for website we want to log in to
        self.base_url = 'https://www.mywebsite.com'
        # login action we want to post data to
        # could be /login or /account/login or something similar
        self.login_action = '/en/login'
        # file for storing cookies
        self.cookie_file = 'login.cookies'

        # user provided username and password
        self.username = username
        self.password = password

        # set up a cookie jar to store cookies
        self.cj = http.cookiejar.MozillaCookieJar(self.cookie_file)

        # set up opener to handle cookies, redirects etc
        self.opener = urllib.request.build_opener(
            urllib.request.HTTPRedirectHandler(),
            urllib.request.HTTPHandler(debuglevel=0),
            urllib.request.HTTPSHandler(debuglevel=0),
            urllib.request.HTTPCookieProcessor(self.cj)
        )

        # pretend we're a web browser and not a python script
        self.opener.addheaders = [('User-agent',
            ('Mozilla/4.0 (compatible; MSIE 6.0; '
            'Windows NT 5.2; .NET CLR 1.1.4322)'))
        ]

        # open the front page of the website to set and save initial cookies
        response = self.opener.open(self.base_url)
        self.cj.save()

        # try and log in to the site
        response = self.login()

        print (response.read())

    # method to do login
    def login(self):

        # parameters for login action
        # may be different for different websites
        # check html source of website for specifics
        login_data = urllib.parse.urlencode({
            'username' : self.username,
            'password' : self.password,
            'remember_me' : True
        })

        # construct the url
        login_url = self.base_url + self.login_action
        # then open it
        response = self.opener.open(login_url.encode(), login_data.encode())
        # save the cookies and return the response
        self.cj.save()
        return response


if __name__ == "__main__":

    args = sys.argv

    # check for username and password
    if len(args) != 3:
        print ("Incorrect number of arguments")
        print ("Argument pattern: username password")
        exit(1)

    username = args[1]
    password = args[2]

    # initialise and login to the website
    WebLogin('mylogin', 'mypass')