code: def choose_boundary():
      
      global BOUNDARY_PREFIX
      if BOUNDARY_PREFIX is None:
          BOUNDARY_PREFIX = "urlfetch"
          try:
              uid = repr(os.getuid())
              BOUNDARY_PREFIX += "." + uid
          except AttributeError:
              pass
          try:
              pid = repr(os.getpid())
              BOUNDARY_PREFIX += "." + pid
          except AttributeError:
              pass
  
      return "%s.%s" % (BOUNDARY_PREFIX, uuid.uuid4().hex)
docs: Generate a multipart boundry.
  
      :returns: A boundary string