Python3标准库：pickle对象串行化(3)

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def preorder_traversal(root, seen=None, parent=None):

"""Generator function to yield the edges in a graph.

"""

if seen is None:

seen = set()

yield (parent, root)

if root in seen:

return

seen.add(root)

for node in root:

recurse = preorder_traversal(node, seen, root)

for parent, subnode in recurse:

yield (parent, subnode)

def show_edges(root):

"Print all the edges in the graph."

for parent, child in preorder_traversal(root):

if not parent:

continue

print('{:>5} -> {:>2} ({})'.format(

parent.name, child.name, id(child)))

# Set up the nodes.

root = Node('root')

a = Node('a')

b = Node('b')

c = Node('c')

# Add edges between them.

root.add_edge(a)

root.add_edge(b)

a.add_edge(b)

b.add_edge(a)

b.add_edge(c)

a.add_edge(a)

print('ORIGINAL GRAPH:')

show_edges(root)

# Pickle and unpickle the graph to create

# a new set of nodes.

dumped = pickle.dumps(root)

reloaded = pickle.loads(dumped)

print('\nRELOADED GRAPH:')

show_edges(reloaded)

重新加载的节点并不是同一个对象，但保持了节点之间的关系，而且如果对象有多个引用，那么只会重新加载这个对象的一个副本。要验证这两点，可以在通过pickle传递节点之前和之后检查节点的id()值。

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