code: def _abbrev_program(program: Program, max_len=10):
      
      program_lines = program.out().splitlines()
      if max_len is not None and len(program_lines) > max_len:
          first_n = max_len // 2
          last_n = max_len - first_n
          excluded = len(program_lines) - max_len
          program_lines = (program_lines[:first_n] + [f'... {excluded} instrs not shown ...']
                           + program_lines[-last_n:])
  
      return '; '.join(program_lines)
docs: Create an abbreviated string representation of a Program.
  
      This will join all instructions onto a single line joined by '; '. If the number of
      instructions exceeds ``max_len``, some will be excluded from the string representation.