Python: Convert a list of python dictionaries to an array of JSON objects

Question

I'm trying to write a function to convert a python list into a JSON array of {"mpn":"list_value"} objects, where "mpn" is the literal string value I need for every object but "list_value" is the value from the python list. I'll use the output of this function for an API get request.

part_nums = ['ECA-1EHG102','CL05B103KB5NNNC','CC0402KRX5R8BB104']

def json_list(list):
    lst = []
    d = {}
    for pn in list:
        d['mpn']=pn
        lst.append(d)
    return json.dumps(lst, separators=(',',':'))

print json_list(part_nums)

This current function is not working and returns last value in the python list for all JSON objects:

>[{"mpn":"CC0402KRX5R8BB104"},{"mpn":"CC0402KRX5R8BB104"},{"mpn":"CC0402KRX5R8BB104"}]

However, of course I need my function to return the unique list values in the objects as such:

>[{"mpn":"ECA-1EHG102"},{"mpn":"CL05B103KB5NNNC"},{"mpn":"CC0402KRX5R8BB104"}]

Bottom line is I don't understand why this function isn't working. I expected I could append a dictionary with a single {key:value} pair to a python list and it wouldn't matter that all of the dictionaries have the same key because they would be independent. Thanks for your help.

move `d = {}` two lines down, inside the `for` – user124114 Jul 03 '12 at 14:12 — user124114, Jul 03 '12 at 14:12

score 31 · Accepted Answer · answered Jul 03 '12 at 14:12

31

You are adding the exact same dictionary to the list. You should create a new dictionary for each item in the list:

json.dumps([dict(mpn=pn) for pn in lst])

answered Jul 03 '12 at 14:12

jfs

399,953
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can we do a reverse of this ? converting a string which is array of json objects to dict ? – divyenduz Nov 11 '14 at 13:37
1

@divyenduz: the "reverse of this" is converting a json text that contains an array of json objects into *list* of dictionaries. Yes, we can: `list_of_dicts = json.loads(json_text)`. If something is unclear, [ask](http://stackoverflow.com/questions/ask) – jfs Dec 01 '14 at 16:52

score 11 · Answer 2 · edited Sep 05 '17 at 21:29

11

As explained by others (in answers) you should create a new dictionary for each item on the list elsewhere you reference always the same dictionary

import json
part_nums = ['ECA-1EHG102','CL05B103KB5NNNC','CC0402KRX5R8BB104']

def json_list(list):
    lst = []
    for pn in list:
        d = {}
        d['mpn']=pn
        lst.append(d)
    return json.dumps(lst)

print json_list(part_nums)

print

[{"mpn": "ECA-1EHG102"}, {"mpn": "CL05B103KB5NNNC"}, {"mpn": "CC0402KRX5R8BB104"}]

edited Sep 05 '17 at 21:29

o12d10

800
3
17
31

answered Jul 03 '12 at 14:24

Xavier Combelle

10,968
5
28
52

Doh, thank you very much for the solution that match my original (inelegant) code. The one line solution is obviously better code but I appreciate you revealing my error. – Bob Jordan Jul 03 '12 at 14:34

score 0 · Answer 3 · edited Feb 26 '20 at 08:50

0

import json
part_nums = ['ECA-1EHG102','CL05B103KB5NNNC','CC0402KRX5R8BB104']

def json_list(list):
    lst = []
    for pn in list:
        d = {}
        d['mpn']=pn
        lst.append(d)
    return json.dumps(lst)

print json_list(part_nums)   # for pyhon2
print (json_list(part_nums)) # for python3

edited Feb 26 '20 at 08:50

4b0

21,981
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answered Feb 26 '20 at 08:45

Mazharul Haque

11
1

Python: Convert a list of python dictionaries to an array of JSON objects

3 Answers3

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