class_docstr: Support Graphite Glat tables
class_docstr_tok: ["Support","Graphite","Glat","tables"]
code: def compileAttributes3(self, attrs):
      if self.hasOctaboxes:
          o = attrs.octabox
          data = sstruct.pack(Glat_format_3_octabox_metrics, o)
          numsub = bin(o.subboxBitmap).count("1")
          for b in range(numsub):
              data += sstruct.pack(
                  Glat_format_3_subbox_entry, o.subboxes[b]
              )
      else:
          data = ""
      return data + self.compileAttributes12(
          attrs, Glat_format_23_entry
      )
  
imports: from fontTools.misc import sstruct
  from fontTools.misc.fixedTools import floatToFixedToStr
  from fontTools.misc.textTools import safeEval
  from functools import partial
  from .None import DefaultTable
  from .None import grUtils
  import struct
label_desc: Use image node_id 7 for calling the table_G__l_a_t obj's underlying member method code with example usage: obj.compileAttributes3(attrs) and returns: unknown