code: def max_command_length():
      
      DEFAULT_MAX_LENGTH = 150000 # lowest seen so far is 200k
      try:
          arg_max = os.sysconf('SC_ARG_MAX')
          env_lines = len(os.environ) * 4
          env_chars = sum([len(x) + len(y) for x, y in os.environ.items()])
          arg_length = arg_max - env_lines - 2048
      except ValueError:
          arg_length = DEFAULT_MAX_LENGTH
      return arg_length if arg_length > 0 else DEFAULT_MAX_LENGTH
docs: get the maximum length of the command line, in bytes, defaulting
      to a conservative number if not set
      http://www.in-ulm.de/~mascheck/various/argmax/