'Looks up the converter for the given parameter.
.. versionadded:: 0.9'

def get_converter(self, variable_name, converter_name, args, kwargs):

    if (converter_name not in self.map.converters):
        raise LookupError(('the    converter    %r    does    not    exist' % converter_name))
    return self.map.converters[converter_name](self.map, *args, **kwargs)
