我的班级有一个字典，例如：
class MyClass(object):
def __init__(self):
self.data = {'a': 'v1', 'b': 'v2'}
然后，我想在MyClass实例中使用字典的键来访问字典，例如：
ob = MyClass()
v = ob.a # Here I expect ob.a returns 'v1'
我知道这应该由__getattr__实现，但是我是Python的新手，我并不完全知道如何实现它。
class MyClass(object):
def __init__(self):
self.data = {'a': 'v1', 'b': 'v2'}
def __getattr__(self, attr):
return self.data[attr]
>>> 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
>>> ob = MyClass()
>>> ob.c = 1
>>> ob.c
1
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.a
1
如果要使用默认参数，可以在其周围编写一个包装器类：
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)
>>> ob = MyClass()
>>> ob.a
'v1'
本文收集自互联网，转载请注明来源。
如有侵权，请联系 [email protected] 删除。
我来说两句