code: def sorted(self):
      self._sorted = []
      for f in self._orig:
          fname = f[0]
          if fname not in self._flags:
              self._visit(f)
  
      return self._sorted
  
file_path: nnabla/python/src/nnabla/utils/converter/nnabla/expander.py
imports: import collections
  import re
  from nnabla.utils import nnabla_pb2
  from nnabla.logger import logger
  from .exporter import rename_square_bracket
label_desc: Use image node_id 3 for calling the _TopologicalSort obj's underlying member method code with example usage: obj.sorted() and returns: self