Use triple braces to avoid shielding {{{var}}}
To avoid escaping, use triple curly braces {{{URL}}}instead of double curly braces{{URL}}
>>> pystache.render('The URL {{{URL}}}', {'URL': 'http://google.com?a=3&b=3'})
u'The URL http://google.com?a=3&b=3'
I tested this in the latest version to date, version 0.5.4
Mustache Documentation
Pystache - Mustache Python, Mustache .
HTML. unescaped HTML, : {{{name}}}.
: https://mustache.imtqy.com/mustache.5.html