code: def from_ranges(ranges, name, data_key, start_key='offset', length_key='length'):
          
          commands = []
          for r in ranges:
              data = r[data_key]
              start = r[start_key]
              stop = start + r[length_key]
              commands.extend(Command.start_stop(name, start, stop, data))
          return commands
docs: Creates a list of commands from a list of ranges. Each range
          is converted to two commands: a start_* and a stop_*.