docs: def save_snaphot(self):
          """Save the current state of the current day bitarray on disk.
  
          Save the internal representation (bitarray) into a binary file using this format:
              filename : name_expiration_2013-01-01.dat
          """
          filename = "%s/%s_%s_%s.dat" % (self.snapshot_path, self.name, self.expiration, self.date)
          with open(filename, 'w') as f:
              f.write(zlib.compress(pickle.dumps(self.current_day_bitarray, protocol=pickle.HIGHEST_PROTOCOL)))