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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _pathology_iterator(graph):
 """Iterate over edges in which either the source or target is a pathology node. :param pybel.BELGraph graph: A BEL graph :rtype: iter """

    for node in itt.chain.from_iterable(graph.edges()):
        if isinstance(node, Pathology):
            yield node