Given a string, encoding it with .encode('base64') is not the same as using base64's b64encode function. I think this is very unclear and unintuitive. 

Here's some example code to demonstrate the problem. Before I attempt to submit a patch, is this done for legacy reasons? Are there any reasons to use one over the other?

import hmac
import hashlib
import base64


signature = hmac.new('secret', 'url', hashlib.sha512).digest()
assert signature.encode('base64') == base64.b64encode(signature)