You need to modify the html.py in Mezzanine.
Modify lib/python3.5/site-packages/mezzanine/utils/html.py
Before:
try: from html.parser import HTMLParser, HTMLParseError from html.entities import name2codepoint except ImportError: # Python 2 from HTMLParser import HTMLParser, HTMLParseError from htmlentitydefs import name2codepoint
After:
try: from html.parser import HTMLParser from html.entities import name2codepoint try: from html.parser import HTMLParseError except ImportError: # Python 3.5+ class HTMLParseError(Exception): pass except ImportError: # Python 2 from HTMLParser import HTMLParser, HTMLParseError from htmlentitydefs import name2codepoint