new_contents: '''
  Workaround for issue with Python mailbox module mis-reading Usenet
  Historical Collection mbox files. Identifies all instances of "from"
  that are *not* in the header, changes them to "xFrom," and writes
  them to a new mailbox.
  '''
  from sys import argv
  
  batch = []
  script, box, newbox = argv
  #box = current mailbox file
  #newbox = new file. Can be .mbox, but doesn't have to be.
  
  with open(box, 'rb') as original, open(newbox, 'wb') as new:
      for line in original:
          if "From " in line:
              num = line[-2]
              #Checks to see if is added Google Groups header
              if num.isdigit() is True:
                  #Skips edit if True
                  batch.append(line)
              else:
                  x = line.replace("From ", "xFrom ")
                  batch.append(x)
          else:
              batch.append(line)
      for line in batch:
          #Writes edited mailbox to new file
          new.writelines(line)
  
subject: Add files via upload