code: def _address_rxp(self, addr):
          
          try:
              addr = to_checksum_address(addr)
              rxp = '(?:0x)?' + pex(address_checksum_and_decode(addr)) + f'(?:{addr.lower()[10:]})?'
              self._extra_keys[pex(address_checksum_and_decode(addr))] = addr.lower()
              self._extra_keys[addr[2:].lower()] = addr.lower()
          except ValueError:
              rxp = addr
          return rxp
docs: Create a regex string for addresses, that matches several representations:
              - with(out) '0x' prefix
              - `pex` version
              This function takes care of maintaining additional lookup keys for substring matches.
              In case the given string is no address, it returns the original string.