嵌套子对象/链式属性上的 getattr 和 setattr?

2022-01-13 00:00:00 python python-2.7 递归 attributes setattr

问题描述

我有一个对象 (Person)，它有多个子对象 (Pet, Residence) 作为属性.我希望能够像这样动态设置这些子对象的属性:

I have an object (Person) that has multiple subobjects (Pet, Residence) as properties. I want to be able to dynamically set the properties of these subobjects like so:

class Person(object):
    def __init__(self):
        self.pet = Pet()
        self.residence = Residence()

class Pet(object):
    def __init__(self,name='Fido',species='Dog'):
        self.name = name
        self.species = species

class Residence(object):
    def __init__(self,type='House',sqft=None):
        self.type = type
        self.sqft=sqft


if __name__=='__main__':
    p=Person()
    setattr(p,'pet.name','Sparky')
    setattr(p,'residence.type','Apartment')
    print p.__dict__

目前我得到了错误的输出:{'pet': <__main__.Pet object at 0x10c5ec050>, 'residence': <__main__.Residence object at 0x10c5ec0d0>, 'pet.name': 'Sparky', 'residence.type': '公寓'}

Currently I get the wrong output: {'pet': <__main__.Pet object at 0x10c5ec050>, 'residence': <__main__.Residence object at 0x10c5ec0d0>, 'pet.name': 'Sparky', 'residence.type': 'Apartment'}

如您所见，不是在 Person 的 Pet 子对象上设置 name 属性，而是一个新属性 pet.name 是在 Person 上创建的.

As you can see, instead of setting the name attribute on the Pet subobject of the Person, a new attribute pet.name is created on the Person.

  • 我无法将person.pet指定为setattr()，因为不同的子对象会被同一个方法设置，解析一些文本并填写如果/当找到相关键时，对象属性.

  • I cannot specify person.pet to setattr() because different sub-objects will be set by the same method, which parses some text and fills in the object attributes if/when a relevant key is found.

有没有一种简单/内置的方法来完成这个?

Is there a easy/builtin way to accomplish this?

或者也许我需要编写一个递归函数来解析字符串并多次调用 getattr() 直到找到必要的子对象然后调用 setattr()?

Or perhaps I need to write a recursive function to parse the string and call getattr() multiple times until the necessary subobject is found and then call setattr() on that found subobject?

解决方案

你可以使用 functools.reduce:

You could use functools.reduce:

import functools

def rsetattr(obj, attr, val):
    pre, _, post = attr.rpartition('.')
    return setattr(rgetattr(obj, pre) if pre else obj, post, val)

# using wonder's beautiful simplification: https://stackoverflow.com/questions/31174295/getattr-and-setattr-on-nested-objects/31174427?noredirect=1#comment86638618_31174427

def rgetattr(obj, attr, *args):
    def _getattr(obj, attr):
        return getattr(obj, attr, *args)
    return functools.reduce(_getattr, [obj] + attr.split('.'))

rgetattr 和 rsetattr 是 getattr 和 setattr 的直接替换，它还可以处理带点的 attr 字符串.

rgetattr and rsetattr are drop-in replacements for getattr and setattr, which can also handle dotted attr strings.

import functools

class Person(object):
    def __init__(self):
        self.pet = Pet()
        self.residence = Residence()

class Pet(object):
    def __init__(self,name='Fido',species='Dog'):
        self.name = name
        self.species = species

class Residence(object):
    def __init__(self,type='House',sqft=None):
        self.type = type
        self.sqft=sqft

def rsetattr(obj, attr, val):
    pre, _, post = attr.rpartition('.')
    return setattr(rgetattr(obj, pre) if pre else obj, post, val)

def rgetattr(obj, attr, *args):
    def _getattr(obj, attr):
        return getattr(obj, attr, *args)
    return functools.reduce(_getattr, [obj] + attr.split('.'))

<小时>

if __name__=='__main__':
    p = Person()
    print(rgetattr(p, 'pet.favorite.color', 'calico'))
    # 'calico'

    try:
        # Without a default argument, `rgetattr`, like `getattr`, raises
        # AttributeError when the dotted attribute is missing
        print(rgetattr(p, 'pet.favorite.color'))
    except AttributeError as err:
        print(err)
        # 'Pet' object has no attribute 'favorite'

    rsetattr(p, 'pet.name', 'Sparky')
    rsetattr(p, 'residence.type', 'Apartment')
    print(p.__dict__)
    print(p.pet.name)
    # Sparky
    print(p.residence.type)
    # Apartment

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