Add one property to json in python

Question

I have the below json, I want to add one more property:

[   {
        "A": 1,
        "B": "str"
    },
    {
        "A": 2,
        "B": "str2"
    },
    {
        "A": 3,
        "B": "str3"
    }
]

So I want something like this:

[   {
        "A": 1,
        "B": "str",
        "C": "X"
    },
    {
        "A": 2,
        "B": "str2",
        "C": "X"
    },
    {
        "A": 3,
        "B": "str3",
        "C": "X"
    }
]

What is the best way to do this?

1. Add the exact same key/val on each occasion, or different ones? 2. Modify existing dicts, or create new ones? 3. Do you have json (as written) or a dict (as shown)? — wim
– wim, Commented Mar 23, 2018 at 4:40

SalGorithm · Accepted Answer · 2018-03-23 04:54:23Z

5

Loop through each dict obj in the list and add required key value pair that you want:

List Before

list1 = [       
   {
        "A": 1,
        "B": "str"
    },
    {
        "A": 2,
        "B": "str2"
    },
    {
        "A": 3,
        "B": "str3"
    }
]

The code

for l in list1:
    l['C'] = 'X'

print(list1)

List After i.e Output

[{'A': 1, 'B': 'str', 'C': 'X'}, {'A': 2, 'B': 'str2', 'C': 'X'}, {'A': 3, 'B': 'str3', 'C': 'X'}]

answered Mar 23, 2018 at 4:54

SalGorithm

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Comments

Carlo Mazzaferro · Accepted Answer · 2018-03-23 04:51:33Z

2

>>> j = [ { "A": 1, "B": "str" }, { "A": 2, "B": "str2" }, { "A": 3, "B": "str3" } ]
>>> [i.update({'C': 'X'}) for i in j]
>>> j
[{'A': 1, 'B': 'str', 'C': 'X'}, {'A': 2, 'B': 'str2', 'C': 'X'}, {'A': 3, 'B': 'str3', 'C': 'X'}]

Or, as per coldspeed's comment:

>>> for item in j:
...     item['C'] = 'X'  
... 
>>> j
[{'A': 1, 'B': 'str', 'C': 'X'}, {'A': 2, 'B': 'str2', 'C': 'X'}, {'A': 3, 'B': 'str3', 'C': 'X'}]

edited Mar 23, 2018 at 4:51

answered Mar 23, 2018 at 4:41

Carlo Mazzaferro

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4 Comments

Stephen Rauch Over a year ago

Any chance you can explain what you did here?

cs95 Over a year ago

I'd advise against using list comprehensions to generate side effects. You're on the right track, but use a loop instead.

cs95 Over a year ago

(responding to your edit) an assignment to i will end up modifying j (print it out and see), because the for loop iterates over the references. In short, the new_list is not required. (also, I did not downvote)

Carlo Mazzaferro Over a year ago

Thanks for the feedback. No worries.

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