Pyhton - Call SOAP API with WSDL, payload and basic authentication from Python

Question

I am attempting to call SOAP API with WSDL, request PAYLOAD, basic authentication using user name and password from Python.

Code spinet is given below. But it is failing to authenticate but same user name and password is working in SOAPUI. Also response contain one attachment. Help me how to get that attachment with some example code.

import base64    
import requests  
from requests.structures import CaseInsensitiveDict    
from requests.auth import HTTPBasicAuth    
url = "https://WSDL URL"    
headersVal = CaseInsensitiveDict()    
headersVal["Content-Type"] = "application/soap+xml"    
headersVal["Authorization"] = 'Basic %s' % base64.b64encode("username:password")    
data = """request Payload"""    
resp = requests.post(url, headers=headersVal, data=data)    
print(resp.status_code)    

Thanks Anish