code: def timestamp_filename(basename, ext=None):
      
      dt = datetime.now().strftime('%Y%m%d-%H%M%S-%f')
      if ext:
          return '%s-%s.%s' % (basename, dt, ext)
      return '%s-%s' % (basename, dt)
docs: Return a string of the form [basename-TIMESTAMP.ext]
      where TIMESTAMP is of the form YYYYMMDD-HHMMSS-MILSEC