HTTP basic authentication not working in python 3.4

Question

I am trying to login to a REST API using HTTP Basic Authentication but it is not working and giving the error

HTTP error 400: Bad Request

Here is my code:

import urllib.parse
import urllib.request
import urllib.response

# create an authorization handler
#auth_handler = urllib.request.HTTPPasswordMgrWithDefaultRealm()
auth_handler = urllib.request.HTTPBasicAuthHandler()


# Add the username and password.
# If we knew the realm, we could use it instead of None.

userName = "username"
passWord  = "pass"
top_level_url = "http URL"
auth_handler.add_password(None, top_level_url, userName,passWord)


# create "opener" (OpenerDirector instance)
opener = urllib.request.build_opener(auth_handler)



# Install the opener.
# Now all calls to urllib.request.urlopen use our opener.
urllib.request.install_opener(opener)

# use the opener to fetch a URL
try:
    result = opener.open(top_level_url)
    #result = urllib.request.urlopen(top_level_url)
    messages = result.read()
    print (messages)  
except IOError as e:
    print (e)

Answer 1

The following python3 code will work:

import urllib.request
import base64
req = urllib.request.Request(download_url)

credentials = ('%s:%s' % (username, password))
encoded_credentials = base64.b64encode(credentials.encode('ascii'))
req.add_header('Authorization', 'Basic %s' % encoded_credentials.decode("ascii"))

with urllib.request.urlopen(req) as response, open(out_file_path, 'wb') as 
out_file:
    data = response.read()
    out_file.write(data)

Answer 2

Updated for Python 3.x compatibility.

The requests library offers a far easier way of making this sort of request:

import requests

response = requests.get('http://service.example.com',
                        auth=requests.auth.HTTPBasicAuth(
                            'username', 'password'))
print(response.text)

In my own testing this works out fine, while a solution involving urllib.request (like yours, or using the code verbatim from the examples in the documentation) will fail to send the Authentication: header.