def touch(file, times=None):
  """Equivalent of unix `touch path`.

  :file The file to touch.
  :times Either a tuple of (atime, mtime) or else a single time to use for both.  If not
  specified both atime and mtime are updated to the current time.
  """
  if times:
    if len(times) > 2:
      raise ValueError('times must either be a tuple of (atime, mtime) or else a single time value '
                       'to use for both.')

    if len(times) == 1:
      times = (times, times)

  with safe_open(file, 'a'):
    os.utime(file, times)