Is is possible to html encode output in AppEngine templates?

Answer 1

Yes, {{ myobject.content | escape }} should help (assuming you mean Django templates -- there's no specific "App Engine" templating system, GAE apps often use the Django templating system); you may need to repeat the | escape part if you want two levels of escaping (as appears to be the case in some but not all of the example you supply).

Answer 2

This is Django's django.utils.html.escape function:

def escape(html):
    """Returns the given HTML with ampersands, quotes and carets encoded."""
    return mark_safe(force_unicode(html).replace('&', '&amp;').replace('<', '&l
t;').replace('>', '&gt;').replace('"', '&quot;').replace("'", '&#39;'))

Also, see here.