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