code: def prune_pre_subset(self, font, options):
      cff = self.cff
      # CFF table must have one font only
      cff.fontNames = cff.fontNames[:1]
  
      if options.notdef_glyph and not options.notdef_outline:
          isCFF2 = cff.major > 1
          for fontname in cff.keys():
              font = cff[fontname]
              _empty_charstring(font, ".notdef", isCFF2=isCFF2)
  
      # Clear useless Encoding
      for fontname in cff.keys():
          font = cff[fontname]
          # https://github.com/fonttools/fonttools/issues/620
          font.Encoding = "StandardEncoding"
  
      return True
  
imports: from fontTools.misc import psCharStrings
  from fontTools import ttLib
  from fontTools.pens.basePen import NullPen
  from fontTools.misc.roundTools import otRound
  from fontTools.misc.loggingTools import deprecateFunction
  from fontTools.subset.util import _add_method, _uniq_sort
label_desc: Use image node_id 3 for calling a global function with example usage: prune_pre_subset(font, options) and returns: True