code: def calc_checksum(sentence):
      
      if sentence.startswith('$'):
          sentence = sentence[1:]
      sentence = sentence.split('*')[0]
      return reduce(xor, map(ord, sentence))
docs: Calculate a NMEA 0183 checksum for the given sentence.
  
      NMEA checksums are a simple XOR of all the characters in the sentence
      between the leading "$" symbol, and the "*" checksum separator.
  
      Args:
          sentence (str): NMEA 0183 formatted sentence