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

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"}]

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])