code: def compile(self, ttFont):
      instanceSize = sstruct.calcsize(FVAR_INSTANCE_FORMAT) + (
          len(self.axes) * 4
      )
      includePostScriptNames = any(
          instance.postscriptNameID != 0xFFFF
          for instance in self.instances
      )
      if includePostScriptNames:
          instanceSize += 2
      header = {
          "version": 0x00010000,
          "offsetToData": sstruct.calcsize(FVAR_HEADER_FORMAT),
          "countSizePairs": 2,
          "axisCount": len(self.axes),
          "axisSize": sstruct.calcsize(FVAR_AXIS_FORMAT),
          "instanceCount": len(self.instances),
          "instanceSize": instanceSize,
      }
      result = [sstruct.pack(FVAR_HEADER_FORMAT, header)]
      result.extend([axis.compile() for axis in self.axes])
      axisTags = [axis.axisTag for axis in self.axes]
      for instance in self.instances:
          result.append(
              instance.compile(axisTags, includePostScriptNames)
          )
      return bytesjoin(result)
  
imports: from fontTools.misc import sstruct
  from fontTools.misc.fixedTools import fixedToFloat, floatToFixed, floatToFixedToStr, strToFixedToFloat
  from fontTools.misc.textTools import Tag, bytesjoin, safeEval
  from fontTools.ttLib import TTLibError
  from .None import DefaultTable
  import struct
label_desc: Use image node_id 2 for calling the table__f_v_a_r obj's underlying member method code with example usage: obj.compile(ttFont) and returns: bytesjoin