+ STR_OPERATORS = {
+ '=': operator.eq,
+ '!=': operator.ne,
+ }
+ str_operator_rex = re.compile(r'''(?x)\s*\[
+ \s*(?P<key>ext|acodec|vcodec|container|protocol)
+ \s*(?P<op>%s)(?P<none_inclusive>\s*\?)?
+ \s*(?P<value>[a-zA-Z0-9_-]+)
+ \s*\]$
+ ''' % '|'.join(map(re.escape, STR_OPERATORS.keys())))
+ m = str_operator_rex.search(format_spec)
+ if m:
+ comparison_value = m.group('value')
+ op = STR_OPERATORS[m.group('op')]