Derive uncompressed key

def unCompressed(self):
        """ Derive uncompressed key """
        public_key = repr(self._pk)
        prefix = public_key[0:2]
        if prefix == "04":
            return public_key
        assert prefix == "02" or prefix == "03"
        x = int(public_key[2:], 16)
        y = self._derive_y_from_x(x, (prefix == "02"))
        key = '04' + '%064x' % x + '%064x' % y
        return key