code: def add_row(self, row):
      chars = self._row_characteristics(row)
      self[chars].append(row)
  
imports: from fontTools.misc.roundTools import noRound, otRound
  from fontTools.misc.intTools import bit_count
  from fontTools.ttLib.tables import otTables
  from fontTools.varLib.models import supportScalar
  from fontTools.varLib.builder import buildVarRegionList, buildVarStore, buildVarRegion, buildVarData
  from functools import partial
  from collections import defaultdict
  from heapq import heappush, heappop
label_desc: Use image node_id 2 for calling the _EncodingDict obj's underlying member method code with example usage: obj.add_row(row) without return types