169 lines
3.3 KiB
Python
169 lines
3.3 KiB
Python
#!/usr/bin/env python
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# -*- encoding: utf-8 -*-
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"""
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Topic: 属性访问代理
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Desc :
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"""
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class A:
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def spam(self, x):
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pass
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def foo(self):
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pass
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class B1:
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"""简单的代理"""
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def __init__(self):
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self._a = A()
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def spam(self, x):
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# Delegate to the internal self._a instance
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return self._a.spam(x)
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def foo(self):
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# Delegate to the internal self._a instance
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return self._a.foo()
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def bar(self):
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pass
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class B2:
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"""使用__getattr__的代理，代理方法比较多时候"""
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def __init__(self):
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self._a = A()
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def bar(self):
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pass
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# Expose all of the methods defined on class A
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def __getattr__(self, name):
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"""这个方法在访问的attribute不存在的时候被调用
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the __getattr__() method is actually a fallback method
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that only gets called when an attribute is not found"""
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return getattr(self._a, name)
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b = B2()
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b.bar() # Calls B.bar() (exists on B)
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b.spam(42) # Calls B.__getattr__('spam') and delegates to A.spam
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# A proxy class that wraps around another object, but
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# exposes its public attributes
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class Proxy:
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def __init__(self, obj):
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self._obj = obj
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# Delegate attribute lookup to internal obj
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def __getattr__(self, name):
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print('getattr:', name)
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return getattr(self._obj, name)
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# Delegate attribute assignment
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def __setattr__(self, name, value):
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if name.startswith('_'):
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super().__setattr__(name, value)
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else:
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print('setattr:', name, value)
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setattr(self._obj, name, value)
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# Delegate attribute deletion
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def __delattr__(self, name):
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if name.startswith('_'):
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super().__delattr__(name)
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else:
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print('delattr:', name)
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delattr(self._obj, name)
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class Spam:
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def __init__(self, x):
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self.x = x
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def bar(self, y):
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print('Spam.bar:', self.x, y)
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# Create an instance
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s = Spam(2)
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# Create a proxy around it
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p = Proxy(s)
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# Access the proxy
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print(p.x) # Outputs 2
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p.bar(3) # Outputs "Spam.bar: 2 3"
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p.x = 37 # Changes s.x to 37
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class ListLike:
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"""__getattr__对于双下划线开始和结尾的方法是不能用的，需要一个个去重定义"""
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def __init__(self):
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self._items = []
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def __getattr__(self, name):
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return getattr(self._items, name)
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# Added special methods to support certain list operations
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def __len__(self):
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return len(self._items)
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def __getitem__(self, index):
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return self._items[index]
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def __setitem__(self, index, value):
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self._items[index] = value
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def __delitem__(self, index):
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del self._items[index]
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a = ListLike()
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a.append(2)
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a.insert(0, 1)
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a.sort()
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print(len(a))
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class A:
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def spam(self, x):
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print('A.spam', x)
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def foo(self):
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print('A.foo')
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class B(A):
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def spam(self, x):
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print('B.spam')
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super().spam(x)
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def bar(self):
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print('B.bar')
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class A:
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def spam(self, x):
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print('A.spam', x)
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def foo(self):
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print('A.foo')
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class B:
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def __init__(self):
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self._a = A()
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def spam(self, x):
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print('B.spam', x)
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self._a.spam(x)
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def bar(self):
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print('B.bar')
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def __getattr__(self, name):
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return getattr(self._a, name) |