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
}}}
----
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