概述
class Parent: def __init__(self,child): self.child = child def __getattr__(self,attr): print("Calling __getattr__: "+attr) if hasattr(self.child,attr): return getattr(self.child,attr) else: raise AttributeError(attr) class Child: def make_statement(self,age=10): print("I am an instance of Child with age "+str(age)) kid = Child() person = Parent(kid) kid.make_statement(5) person.make_statement(20)
可以显示,函数调用person.make_statement(20)通过Parent的__getattr__函数调用Child.make_statement函数.在__getattr__函数中,我可以在子实例的相应函数被调用之前打印出属性.到目前为然这么清楚
但是调用person.make_statement(20)的参数怎么通过__getattr__?我可以在__getattr__函数中打印出数字“20”吗?
如果你要删除()调用,它仍然可以工作;我们可以存储方法并单独打电话给20打印:
>>> person.make_statement Calling __getattr__: make_statement <bound method Child.make_statement of <__main__.Child instance at 0x10db5ed88>> >>> ms = person.make_statement Calling __getattr__: make_statement >>> ms() I am an instance of Child with age 10
def __getattr__(self,attr): print("Calling __getattr__: "+attr) if hasattr(self.child,attr): def wrapper(*args,**kw): print('called with %r and %r' % (args,kw)) return getattr(self.child,attr)(*args,**kw) return wrapper raise AttributeError(attr)
现在这样做:
>>> person.make_statement(20) Calling __getattr__: make_statement called with (20,) and {} I am an instance of Child with age 20
总结
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