The requests library has Basic Auth support and will encode it for you automatically. You can test it out by running the following in a python repl
from requests.auth import HTTPBasicAuth
r = requests.post(api_URL, auth=HTTPBasicAuth('user', 'pass'), data=payload)
You can confirm this encoding by typing the following.
r.request.headers['Authorization']
outputs:
u'Basic c2RhZG1pbmlzdHJhdG9yOiFTRG0wMDY4'