How do i delete an element of a json object with python?

Question

I'm trying to delete elements from _notes that have _type as 1, but i keep getting an error and I'm not sure what it means, nor do I know how to fix it.. can anyone help me?

My trimmed JSON:

{
    "_notes": [
        {
            "_time": 10,
            "_lineIndex": 2,
            "_lineLayer": 0,
            "_type": 0,
            "_cutDirection": 7
        },
        {
            "_time": 12,
            "_lineIndex": 2,
            "_lineLayer": 0,
            "_type": 1,
            "_cutDirection": 1
        },
        {
            "_time": 14,
            "_lineIndex": 2,
            "_lineLayer": 1,
            "_type": 1,
            "_cutDirection": 0
        }
    ]
}

My python script:

#!/usr/bin/python3

import json
obj = json.load(open("ExpertPlusStandardd.dat"))

for i in range(len(obj["_notes"])):
    print(obj["_notes"][i]["_type"])
    if obj["_notes"][i]["_type"] == 1:
        obj.pop(obj["_notes"][i])

open("test.dat", "w").write(
    json.dumps(obj, indent=4, separators=(',', ': '))
)

Error: Traceback (most recent call last): File "C:\programming\python\train_one_hand\run.py", line 9, in <module> obj.pop(obj["_notes"][i]) TypeError: unhashable type: 'dict'

always put full error message (starting at word "Traceback") in question (not in comments) as text (not screenshot, not link to external portal). There are other useful information. — furas
– furas, Commented Jul 17, 2022 at 14:15
as for me this JSON data can't give your error message - you have to check what you really have in your file "ExpertPlusStandardd.dat" — furas
– furas, Commented Jul 17, 2022 at 14:16
i copied the contents of ExpertPlusStandardd.dat into my question — miitchel
– miitchel, Commented Jul 17, 2022 at 14:17
it is wrong idea to remove (pop) item from object which you use in for-loop - because it moves items on list and later it tries to use index which doesn't exists any more. You should rather create new JSON and put in this JSON elements which you want to keep — furas
– furas, Commented Jul 17, 2022 at 14:20

Himanshu Poddar · Accepted Answer · 2022-07-17 14:21:33Z

2

It is usually a bad idea to delete from a list that you're iterating. Reverse iterating avoids some of the pitfalls, but it is much more difficult to follow code that does that, so usually you're better off using a list comprehension or filter.

obj["_notes"] = [x for x in obj["_notes"] if x["_type"] != 1]

This gives us the expected output :

{'_notes': 
   [
       {
            '_time': 10, 
            '_lineIndex': 2, 
            '_lineLayer': 0, 
            '_type': 0, 
            '_cutDirection': 7
       }
   ]
}

answered Jul 17, 2022 at 14:21

Himanshu Poddar

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