docs: def btc_script_to_hex(script):
      """ Parse the string representation of a script and return the hex version.
          Example: "OP_DUP OP_HASH160 c629...a6db OP_EQUALVERIFY OP_CHECKSIG"
      """
  
      hex_script = ''
      parts = script.split(' ')
      for part in parts:
          if part[0:3] == 'OP_':
              value = OPCODE_VALUES.get(part)
              if not value:
                  raise ValueError("Unrecognized opcode {}".format(part))
  
              hex_script += "%0.2x" % value
  
          elif hashing.is_hex(part):
              hex_script += '%0.2x' % hashing.count_bytes(part) + part
  
          else:
              raise Exception('Invalid script - only opcodes and hex characters allowed.')
  
      return hex_script