graph.py 文件源码

def __init__(self, terms):
        super(TermGraph, self).__init__(self)

        self._frozen = False
        parents = set()
        for term in itervalues(terms):
            self._add_to_graph(term, parents, extra_rows=0)
            # No parents should be left between top-level terms.
            assert not parents

        self._outputs = terms
        self._ordered = topological_sort(self)

        # Mark that no more terms should be added to the graph.
        self._frozen = True