old_contents: def byte_format(n, roundto=2):
      """
      Runtime: O(1)
      """
      units = ["B", "KB", "MB", "GB", "TB", "PB"] # ...
      id = 0
      factor = 1024 # or 1000
      while n > factor:
          n = float(n) / factor
          id += 1
      n = "%.{0}f".format(roundto) % n
      return "{0} {1}".format(n, units[id])
  
  
  print byte_format(156833213) # "149.57 MB"
  print byte_format(8101)      # "7.91 KB"
  print byte_format(12331, 3)  # "12.042 KB"
  
new_contents: def byte_format(n, roundto=2):
      """
      Runtime: O(n)
      """
      units = ["B", "KB", "MB", "GB", "TB", "PB"]  # ...
      id = 0
      factor = 1024  # or 1000
      while n > factor:
          n = float(n) / factor
          id += 1
      n = "%.{0}f".format(roundto) % n
      return "{0} {1}".format(n, units[id])
  
  
  print byte_format(156833213)  # "149.57 MB"
  print byte_format(8101)      # "7.91 KB"
  print byte_format(12331, 3)  # "12.042 KB"
  
subject: Fix typo