@staticmethod
def _normalize_byte_sig(byte_sig: str) ->str:
    """Adds a leading 0x to the byte signature if it's not already there.

        :param byte_sig: 4-byte signature string
        :return: normalized byte signature string
        """
    if not byte_sig.startswith('0x'):
        byte_sig = '0x' + byte_sig
    if not len(byte_sig) == 10:
        raise ValueError('Invalid byte signature %s, must have 10 characters',
            byte_sig)
    return byte_sig
