65 lines
1.3 KiB
Python
65 lines
1.3 KiB
Python
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#!/usr/bin/env python
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# -*- encoding: utf-8 -*-
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"""
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Topic: 弱引用
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Desc :
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"""
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import weakref
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class Node:
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def __init__(self, value):
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self.value = value
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self._parent = None
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self.children = []
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def __repr__(self):
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return 'Node({!r:})'.format(self.value)
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# property that manages the parent as a weak-reference
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@property
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def parent(self):
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return None if self._parent is None else self._parent()
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@parent.setter
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def parent(self, node):
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self._parent = weakref.ref(node)
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def add_child(self, child):
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self.children.append(child)
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child.parent = self
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# Class just to illustrate when deletion occurs
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class Data:
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def __del__(self):
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print('Data.__del__')
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# Node class involving a cycle
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class Node1:
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def __init__(self):
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self.data = Data()
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self.parent = None
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self.children = []
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def add_child(self, child):
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self.children.append(child)
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child.parent = self
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a = Data()
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del a
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# print(a) NameError: name 'a' is not defined
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a = Node1()
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del a
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# print(a)
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a = Node1()
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a.add_child(Node1())
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print('--------last del start------------')
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del a # Not deleted (no message)
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print('--------last del end------------')
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# print(a)
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print('11111111111111111')
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