class A(object):
    def __init__(self, a, b):
        self.a1 = a
        self.b1 = b
        print('init')
    def mydefault(self, *args):
        print('default:' + str(args[0]))
    def __getattr__(self, name):
        print("other fn:", name)
        return self.mydefault
a1 = A(10, 20)
a1.fn1(33)
a1.fn2('hello')

運行結(jié)果：

init
other fn: fn1
default:33
other fn: fn2
default:hello

第16行調(diào)用fn1屬性時，查找不到次屬性，程序調(diào)用__getattr__方法

用__getattr__方法可以處理調(diào)用屬性異常

class Student(object):
    def __getattr__(self, attrname):
        if attrname == "age":
            return 'age:40'
        else:
            raise AttributeError(attrname)
x = Student()
print(x.age)  # 40
print(x.name)

這里定義一個Student類和實例x，并沒有屬性age,當(dāng)執(zhí)行x.age,就調(diào)用_getattr_方法動態(tài)創(chuàng)建一個屬性，執(zhí)行x.name時，__getattr__方法沒有對其處理，拋出異常

age:40
  File "XXXX.py", line 10, in <module>
    print(x.name)
  File "XXXX.py", line 6, in __getattr__
    raise AttributeError(attrname)
AttributeError: name

下面展示一個_getattr_經(jīng)典應(yīng)用的例子，可以調(diào)用dict的鍵值對

class ObjectDict(dict):
    def __init__(self, *args, **kwargs):
        super(ObjectDict, self).__init__(*args, **kwargs)
    def __getattr__(self, name):
        value = self[name]
        if isinstance(value, dict):
            value = ObjectDict(value)
        return value
if __name__ == '__main__':
    od = ObjectDict(asf = {'a': 1}, d = True)
    print(od.asf, od.asf.a)  # {'a': 1} 1
    print(od.d)  # True

以上就是Python的getattr方法學(xué)習(xí)使用示例的詳細內(nèi)容，更多關(guān)于Python getattr方法的資料請關(guān)注腳本之家其它相關(guān)文章！

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