docs: def print_mem(unit="MB"):
      """Show the proc-mem-cost with psutil, use this only for lazinesssss.
  
      :param unit: B, KB, MB, GB.
      """
      try:
          import psutil
  
          B = float(psutil.Process(os.getpid()).memory_info().vms)
          KB = B / 1024
          MB = KB / 1024
          GB = MB / 1024
          result = vars()[unit]
          print_info("memory usage: %.2f(%s)" % (result, unit))
          return result
      except ImportError:
          print_info("pip install psutil first.")