code: def compile(self, ttFont):
      dataList = []
      dataList.append(
          sstruct.pack(smallGlyphMetricsFormat, self.metrics)
      )
      dataList.append(struct.pack(">L", len(self.imageData)))
      dataList.append(self.imageData)
      return bytesjoin(dataList)
  
imports: from fontTools.misc.textTools import bytesjoin
  from fontTools.misc import sstruct
  from .None import E_B_D_T_
  from .BitmapGlyphMetrics import BigGlyphMetrics, bigGlyphMetricsFormat, SmallGlyphMetrics, smallGlyphMetricsFormat
  from .E_B_D_T_ import BitmapGlyph, BitmapPlusSmallMetricsMixin, BitmapPlusBigMetricsMixin
  import struct
label_desc: Use image node_id 2 for calling the cbdt_bitmap_format_17 obj's underlying member method code with example usage: obj.compile(ttFont) and returns: bytesjoin