Python链式JSON中具有列表元素的get()方法 [英] Python Chained get() Method With List Element inside JSON

问题描述

[Python 2.7]

[Python 2.7]

我有一个JSON源，它并不总是返回期望键的完整列表.我正在使用链接的gets()来解决这个问题.

I have a JSON source that doesn't always return the full list of expected keys. I'm using chained gets() to address this.

d = {'a': {'b': 1}}

print(d.get('a', {}).get('b', 'NA'))
print(d.get('a', {}).get('c', 'NA'))

>>> 1
>>> NA

但是，列表中有一些字典:

However, some dicts are in a list:

d = {'a': {'b': [{'c': 2}]}}

print(d['a']['b'][0]['c'])

>>> 2

我不能使用get()方法来解决这个问题，因为列表不支持get()属性:

I can't use a get() method to account for this because lists don't support the get() attribute:

d.get('a', {}).get('b', []).get('c', 'NA')

>>> AttributeError: 'list' object has no attribute 'get'

除了捕获数百个潜在的KeyError错误之外，还有一种更好的方法来解决潜在的['c']缺失(类似于上面链接的get()构造的方式)吗?

Beyond trapping the hundreds of potential KeyErrors, is there a preferred method to account for the potential missing ['c'] (in similar fashion to the chained get() construct above)?

推荐答案

我同意@stovfl的观点，即编写自己的查找函数是必经之路.虽然，我认为不需要递归实现.以下应该可以很好地工作:

I agree with @stovfl that writing your own lookup function is the way to go. Although, I don't think a recursive implementation is necessary. The following should work well enough:

def nested_lookup(obj, keys, default='NA'):
    current = obj
    for key in keys:
        current = current if isinstance(current, list) else [current]
        try:
            current = next(sub[key] for sub in current if key in sub)
        except StopIteration:
            return default
    return current


d = {'a': {'b': [{'c': 2}, {'d': 3}]}}

print nested_lookup(d, ('a', 'b', 'c'))  # 2
print nested_lookup(d, ('a', 'b', 'd'))  # 3
print nested_lookup(d, ('a', 'c'))       # NA

类方法似乎不太好，因为您将创建许多不必要的对象，并且如果您试图查找不是叶子的节点，那么您将结束使用自定义对象而不是实际的节点对象.

The class approach doesn't seem great because you're going to be creating a lot of unnecessary objects and if you're ever trying to lookup a node that isn't a leaf, then you're going to wind up with a custom object rather than the actual node object.

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