class_docstr: Provides functionality to topologically sort a graph of hashable nodes
code: def __init__(self, graph=None):
      self._node2info = {}
      self._ready_nodes = None
      self._npassedout = 0
      self._nfinished = 0
  
      if graph is not None:
          for node, predecessors in graph.items():
              self.add(node, *predecessors)
  
file_path: cpython/Lib/graphlib.py
imports: from types import GenericAlias
label_desc: Use image node_id 1 to create a new TopologicalSorter object  with example: obj = TopologicalSorter(graph)