Thrift requires the params and headers dict values to only contain str values.

def _dict_to_map_str_str(self, d):
        """
        Thrift requires the params and headers dict values to only contain str values.
        """
        return dict(map(
            lambda (k, v): (k, str(v).lower() if isinstance(v, bool) else str(v)),
            d.iteritems()
        ))