Sounds like you want to load a dictionary from json, add new key values and write it back. If that's the case, you can do this:

with open('python_dictionary.json','r+') as f:
    dic = json.load(f)
    dic.update(new_dictionary)
    json.dump(dic, f)

(mode is 'r+' for reading and writing, not appending because you're re-writing the entire file)

If you want to do the append thing, along with json.dumps, I guess you'd have to remove the first { from the json.dumps string before appending. Something like:

with open('python_dictionary.json','a') as f:
    str = json.dumps(new_dictionary).replace('{', ',', 1)
    f.seek(-2,2)
    f.write(str)

There are several questions here. The main points worth mentioning:

• Use can use a list to hold your arguments and use *args to unpack when you supply them to add_entry.
• To check / avoid duplicates, you can use set to track items already added.
• For writing to JSON, now you have a list, you can simply iterate your list and write in one function at the end.

Putting these aspects together:

import json

res = []
seen = set()

def add_entry(res, name, element, type):

    # check if in seen set
    if (name, element, type) in seen:
        return res

    # add to seen set
    seen.add(tuple([name, element, type]))

    # append to results list
    res.append({'name': name, 'element': element, 'type': type})

    return res

args = ['xyz', '4444', 'test2']

res = add_entry(res, *args)  # add entry - SUCCESS
res = add_entry(res, *args)  # try to add again - FAIL

args2 = ['wxy', '3241', 'test3']

res = add_entry(res, *args2)  # add another - SUCCESS

Result:

print(res)

[{'name': 'xyz', 'element': '4444', 'type': 'test2'},
 {'name': 'wxy', 'element': '3241', 'type': 'test3'}]

Writing to JSON via a function:

def write_to_json(lst, fn):
    with open(fn, 'a', encoding='utf-8') as file:
        for item in lst:
            x = json.dumps(item, indent=4)
            file.write(x + '\n')

#export to JSON
write_to_json(res, 'elements.json')

You have to read your JSON file and then convert it to list instead of dict. Then you just need to append to that list and overwrite your JSON file.

import json

data = json.load(open('data.json'))

# convert data to list if not
if type(data) is dict:
    data = [data]

# append new item to data lit
data.append({
  "user": "user2",
  "id": "21780"
})

# write list to file
with open('data.json', 'w') as outfile:
    json.dump(data, outfile)

But now I want to add a key/val pair to this dictionary

You can index the list and update that dictionary:

temp['logs'][0].update({'new_key': 'new_value'})

I found simple solution:

Append JSON file with new data:

import os, json

with open('data.json', 'a') as fp:
    json.dump(j_data, fp, indent = 2)
fp.close()

f = open('data.json','r')
old_data = f.read()
f.close()

search " ][ " and replace it with " , "

new_data = old_data.replace("][", ",")

save as new file

f = open('data_new.json','w')
f.write(new_data)
f.close()

remove old file and rename new file

os.remove('data.json')
os.rename('data_new.json', 'data.json')