Format attributes including {} tags with arguments.

def format(self, attrs, args=None):
        """Format attributes including {} tags with arguments."""
        if args is None:
            return attrs

        out = {}
        for key, val in attrs.items():
            mba = {'indexer': 'annual'}
            # Add formatting {} around values to be able to replace them with _attrs_mapping using format.
            for k, v in args.items():
                if isinstance(v, six.string_types) and v in self._attrs_mapping.get(key, {}).keys():
                    mba[k] = '{{{}}}'.format(v)
                elif isinstance(v, dict):
                    if v:
                        dk, dv = v.copy().popitem()
                        if dk == 'month':
                            dv = 'm{}'.format(dv)
                        mba[k] = '{{{}}}'.format(dv)
                else:
                    mba[k] = int(v) if (isinstance(v, float) and v % 1 == 0) else v

            out[key] = val.format(**mba).format(**self._attrs_mapping.get(key, {}))

        return out