Retreive JSON Keys In Python

Question

My goal is to iterate through every element in classes and add the value of class in classes into a new list.

JSON Structure:

{
    "images": [
      {
        "classifiers": [
          {
            "classes": [
              {
                "class": "street",
                "score": 0.846
              },
              {
                "class": "road",
                "score": 0.85
              }
            ]
          }
        ]
      }
   ]
}

In the above JSON example, the new list should contain:

{'street','road'}

I tried to iterate over json_data['images'][0]['classifiers']['classes'] and for each one list.append() the value of class.

list = list()
def func(json_data):
    for item in json_data['images'][0]['classifiers']['classes']:
        list.append(item['class'])
    return(list)

I am receiving a TypeError which is:

TypeError: list indices must be integers or slices, not str

What I am getting from this TypeError is that it attempts to add a string to the list but list.append() does not accept a string as a paramet. I need to somehow convert the string into something else.

My question is what should I convert the string into so that list.append() will accept it as a parameter?

Thanks for showing us your input & expected output. Now show us the code you've written to do this, and explain where you're stuck. — PM 2Ring
– PM 2Ring, Commented Jul 25, 2017 at 18:14
I keeep getting TypeError: list indices must be integers or slices, not str and using that error and trying things on StackOverflow to fix that error are not working. — James
– James, Commented Jul 25, 2017 at 18:16
classifiers and classes are also lists. json_data['images'][0]['classifiers'][0]['classes']: — roganjosh
– roganjosh, Commented Jul 25, 2017 at 18:18
return set(lst) I think. If that is what you expect I'll have a go at writing an answer on my phone - always fun - so you can close this. — roganjosh
– roganjosh, Commented Jul 25, 2017 at 18:29

roganjosh · Accepted Answer · 2017-07-25 18:42:33Z

3

The first issue is that classifiers is also a list, so you need an additional index to get at classes. This will work:

for item in json_data['images'][0]['classifiers'][0]['classes']:

Second, you want the result as a set not a list, so you can do: return set(lst). Note that sets are unordered, so don't expect the ordering of items to match that of the list.

edited Jul 25, 2017 at 18:42

answered Jul 25, 2017 at 18:36

roganjosh

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7 Comments

James Over a year ago

How do I make it ordered?

roganjosh Over a year ago

Why do you need it to be both a set and ordered before we go down that route?

James Over a year ago

It actully does not need to be a set. It can be a list

James Over a year ago

I just need it to have the {}

James Over a year ago

What does this mean? Doing if ['images'][0]['classifiers'][0]["classes"] not in json_data: Gives me TypeError: string indices must be integers

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