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
– user124114

2012-07-03 14:12:39 +00:00
Commented Jul 3, 2012 at 14:12 — user124114
– user124114, Commented Jul 3, 2012 at 14:12

jfs · Accepted Answer · 2012-07-03 14:12:45Z

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 3, 2012 at 14:12

jfs

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2 Comments

divyenduz Over a year ago

can we do a reverse of this ? converting a string which is array of json objects to dict ?

jfs Over a year ago

@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

o12d10 · Accepted Answer · 2017-09-05 21:29:09Z

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 5, 2017 at 21:29

o12d10

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answered Jul 3, 2012 at 14:24

Xavier Combelle

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1 Comment

Bob Jordan Over a year ago

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.

4b0 · Accepted Answer · 2020-02-26 08:50:00Z

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, 2020 at 8:50

4b0

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answered Feb 26, 2020 at 8:45

Mazharul Haque

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