Python：如何实现__getattr __（）？

Python：如何实现__getattr __（）？

class MyClass(object):    def __init__(self):        self.data = {'a': 'v1', 'b': 'v2'}    def __getattr__(self, attr):        return self.data[attr]

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>>> ob = MyClass()>>> v = ob.a>>> v'v1'

__setattr__

不过在实施时要小心，您将需要进行一些修改：

class MyClass(object):    def __init__(self):        # prevents infinite recursion from self.data = {'a': 'v1', 'b': 'v2'}        # as now we have __setattr__, which will call __getattr__ when the line        # self.data[k] tries to access self.data, won't find it in the instance         # dictionary and return self.data[k] will in turn call __getattr__        # for the same reason and so on.... so we manually set data initially        super(MyClass, self).__setattr__('data', {'a': 'v1', 'b': 'v2'})    def __setattr__(self, k, v):        self.data[k] = v    def __getattr__(self, k):        # we don't need a special call to super here because getattr is only         # called when an attribute is NOT found in the instance's dictionary        try: return self.data[k]        except KeyError: raise AttributeError

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>>> ob = MyClass()>>> ob.c = 1>>> ob.c1

如果您不需要设置属性，只需使用namedtuple例如。

>>> from collections import namedtuple>>> MyClass = namedtuple("MyClass", ["a", "b"])>>> ob = MyClass(a=1, b=2)>>> ob.a1

如果您想要默认参数，则可以围绕它编写包装类：

class MyClass(namedtuple("MyClass", ["a", "b"])):    def __new__(cls, a="v1", b="v2"):        return super(MyClass, cls).__new__(cls, a, b)

或者作为函数看起来更好：

def MyClass(a="v1", b="v2", cls=namedtuple("MyClass", ["a", "b"])):    return cls(a, b)

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>>> ob = MyClass()>>> ob.a'v1'