append data to an existing json file - json

Question

Appreciate if someone can point me to the right direction in here, bit new to python :)
I have a json file that looks like this:
[
{
"user":"user5",
"games":"game1"
},
{
"user":"user6",
"games":"game2"
},
{
"user":"user5",
"games":"game3"
},
{
"user":"user6",
"games":"game4"
}
]
And i have a small csv file that looks like this:
module_a,module_b
10,20
15,16
1,11
2,6
I am trying to append the csv data into the above mentioned json so it looks this, keeping the order as it is:
[
{
"user":"user5",
"module_a":"10",
"games":"game1",
"module_b":"20"
},
{
"user":"user6",
"module_a":"15",
"games":"game2",
"module_b":"16"
},
{
"user":"user5",
"module_a":"1",
"games":"game3",
"module_b":"11"
},
{
"user":"user6",
"module_a":"2",
"games":"game4",
"module_b":"6"
}
]
what would be the best approach to achive this keep the output order as it is.
Appreciate any guidance.

Answer 1

JSON specification doesn't prescribe orderness and it won't be enforced (unless it's a default mode of operation of the underlying platform) by any JSON parser so going a long way just to keep the order when processing JSON files is usually pointless. To quote:
An object is an unordered collection of zero or more name/value
pairs, where a name is a string and a value is a string, number,
boolean, null, object, or array.
...
JSON parsing libraries have been observed to differ as to whether or
not they make the ordering of object members visible to calling
software. Implementations whose behavior does not depend on member
ordering will be interoperable in the sense that they will not be
affected by these differences.
That being said, if you really insist on order, you can parse your JSON into a collections.OrderedDict (and write it back from it) which will allow you to inject data at specific places while keeping the overall order. So, first load your JSON as:
import json
from collections import OrderedDict
with open("input_file.json", "r") as f: # open the JSON file for reading
json_data = json.load(f, object_pairs_hook=OrderedDict) # read & parse it
Now that you have your JSON, you can go ahead and load up your CSV, and since there's not much else to do with the data you can immediately apply it to the json_data. One caveat, tho - since there is no direct map between the CSV and the JSON one has to assume index as being the map (i.e. the first CSV row being applied to the first JSON element etc.) so we'll use enumerate() to track the current index. There is also no info on where to insert individual values so we'll assume that the first column goes after the first JSON object entry, the second goes after the second entry and so on, and since they can have different lenghts we'll use itertools.izip_longest() to interleave them. So:
import csv
from itertools import izip_longest # use zip_longest on Python 3.x
with open("input_file.csv", "rb") as f: # open the CSV file for reading
reader = csv.reader(f) # build a CSV reader
header = next(reader) # lets store the header so we can get the key values later
for index, row in enumerate(reader): # enumerate and iterate over the rest
if index >= len(json_data): # there are more CSV rows than we have elements in JSO
break
row = [(header[i], v) for i, v in enumerate(row)] # turn the row into element tuples
# since collections.OrderedDict doesn't support random access by index we'll have to
# rebuild it by mixing in the CSV elements with the existing JSON elements
# use json_data[i].items() on Python 3.x
data = (v for p in izip_longest(json_data[index].iteritems(), row) for v in p)
# then finally overwrite the current element in json_data with a new OrderedDict
json_data[index] = OrderedDict(data)
And with our CSV data nicely inserted into the json_data, all that's left is to write back the JSON (you may overwrite the original file if you wish):
with open("output_file.json", "w") as f: # open the output JSON file for writing
json.dump(json_data, f, indent=2) # finally, write back the modified JSON
This will produce the result you're after. It even respects the names in the CSV header so you can replace them with bob and fred and it will insert those keys in your JSON. You can even add more of them if you need more elements added to your JSON.
Still, just because it's possible, you really shouldn't rely on JSON orderness. If it's user-readibility you're after, there are far more suitable formats with optional orderness like YAML.