I am trying to use Zeep to implement a SOAP client, as it seems the only maintained library at the moment:
For Basic Access Authentication you can use the HTTPBasicAuth class from the requests module, as explained on Zeep documentation http://docs.python-zeep.org/en/master/transport.html:
from requests.auth import HTTPBasicAuth # or HTTPDigestAuth, or OAuth1, etc.
from zeep import Client
from zeep.transports import Transport
client = Client('http://my-endpoint.com/production.svc?wsdl',
transport=Transport(http_auth=HTTPBasicAuth(user, password)))