是否有内置的dict.get()的递归版本? [英] Is there a recursive version of the dict.get() built-in?

问题描述

我有一个嵌套的字典对象，并且希望能够检索具有任意深度的键的值.我可以通过将dict子类化:

I have a nested dictionary object and I want to be able to retrieve values of keys with an arbitrary depth. I'm able to do this by subclassing dict:

>>> class MyDict(dict):
...     def recursive_get(self, *args, **kwargs):
...         default = kwargs.get('default')
...         cursor = self
...         for a in args:
...             if cursor is default: break
...             cursor = cursor.get(a, default)
...         return cursor
... 
>>> d = MyDict(foo={'bar': 'baz'})
>>> d
{'foo': {'bar': 'baz'}}
>>> d.get('foo')
{'bar': 'baz'}
>>> d.recursive_get('foo')
{'bar': 'baz'}
>>> d.recursive_get('foo', 'bar')
'baz'
>>> d.recursive_get('bogus key', default='nonexistent key')
'nonexistent key'

但是，我不需要子类来获得此行为.是否有一些具有等效或相似行为的内置方法?如果没有，是否有任何标准或外部模块可以提供这种功能?

However, I don't want to have to subclass dict to get this behavior. Is there some built-in method that has equivalent or similar behavior? If not, are there any standard or external modules that provide this behavior?

我目前正在使用Python 2.7，尽管我也很好奇也听说过3.x解决方案.

I'm using Python 2.7 at the moment, though I would be curious to hear about 3.x solutions as well.

推荐答案

执行此操作的一种非常常见的模式是使用空dict作为默认值:

A very common pattern to do this is to use an empty dict as your default:

d.get('foo', {}).get('bar')

如果您有多个键，则可以使用reduce(请注意，在Python 3中，必须导入reduce:from functools import reduce)多次应用该操作

If you have more than a couple of keys, you could use reduce (note that in Python 3 reduce must be imported: from functools import reduce) to apply the operation multiple times

reduce(lambda c, k: c.get(k, {}), ['foo', 'bar'], d)

当然，您应该考虑将其包装到一个函数(或方法)中:

Of course, you should consider wrapping this into a function (or a method):

def recursive_get(d, *keys):
    return reduce(lambda c, k: c.get(k, {}), keys, d)

这篇关于是否有内置的dict.get()的递归版本?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！