When using Python 3, there is similar problem as in botocore (boto/botocore#319):

~/project_path/venv/lib/python3.4/site-packages/boto/auth.py:92: DeprecationWarning: encodestring() is a deprecated alias, use encodebytes()
return base64.encodestring(new_hmac.digest()).decode('utf-8').strip()

Will send pull request soon.