只有定义了值，Python字典才会更新 [英] Python dictionary update only if value is defined

问题描述

如果我运行以下代码：

import json

foo = [
    {
        "name": "Bob",
        "occupation": "",
        "standing": "good",
        "locations": ["California"],
        "meta": { "last_updated": "2018-01-15" }
    },
    {
        "name": "",
        "occupation": "Carpenter",
        "standing": "bad",
        "locations": ["Arizona"],
        "meta": { "last_updated": "2018-01-15", "email": "[e-mail]" }
    },
]

output = {}
for i in foo:
    output.update(i)
print json.dumps(output)

最终输出是：

{
    "locations": [
        "Arizona"
    ],
    "meta": {
        "email": "[e-mail]",
        "last_updated": "2018-01-15"
    },
    "name": "",
    "occupation": "Carpenter",
    "standing": "bad"
}

那很好。但是，我试图弄清楚如何将一个函数传递给update方法，该方法基本上说：只有在定义了值或不为空的情况下，才进行更新。因此，在第一次迭代中，名称为 Bob，而在第二次迭代中，名称仍为Bob，因为名称实际上是未定义的。

That's pretty good. However, I'm trying to figure out how I can pass a function to the update method that basically says, "Only update if the value is defined/not empty." Therefore, on the first iteration name is "Bob", and on the second iteration name remains Bob since name is essentially undefined.

最终输出如下所示：

{
    "locations": [
        "Arizona"
    ],
    "meta": {
        "email": "[e-mail]",
        "last_updated": "2018-01-15"
    },
    "name": "Bob",
    "occupation": "Carpenter",
    "standing": "bad"
}

推荐答案

您可以使用以下内容过滤正在更新的新词典：

You could filter the new dictionary you are updating on, with something like:

b = {'bla': '', 'b': 77, 'c': '9'}
new_b = { k: v for k,v in b.items() if v }

new_b 不会再有 bla 作为元素。

因此，在您的情况下：

for i in foo:
    output.update({ k: v for k,v in i.items() if v })

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