CODEWITHSUNDEEP
pythonjson
hfires
hfires

Reputation: 123

How to assign values to a python dictionary inside a list

i'm trying to assign values to a dictionary that is contained within a python list. My logic seems to work fine except it is assigning 'None' values in the first iteration of the loop. The rest of the iterations assign the values as expected.

The goal is to loop through this json and create hundreds or thousands of objects for the "trend_values" key. This json is assgined to a variable called 'data' using json.load(filename) 

{
  "machine_id": null,
  "trend_values": [
    {
      "name": null,
      "tag": null,
      "units": null,
      "value": null
    }
  ],
  "schedule_date": null,
  "message_ids": [
    null
  ]
}

I am trying to accomplish this by using the below code.

    data['machine_id'] = rand_machine_id
    for item in data:
       rand_tag = get_machine_tag()
       rand_unit = get_machine_unit()
       rand_int = random.randint(1,1000000)
           data['trend_values'].append(({
        'name' : device_name,
        'tag': rand_tag,
        'units': rand_unit,
        'value': rand_int}))
    data['schedule_date'] = date_time
    data['message_ids'] = message_id

I know the above logic isn't correct because the loop assigns 'None' values in the first iteration as show below.

{"machine_id": "qleryoajmm", 
    "trend_values": 
     [
      {"name": null, "tag": null, "units": null, "value": null}, 
      {"name": "compressor", "tag": "hwc", "units": "mrqa", "value": 129859}, 
      {"name": "compressor", "tag": "clb", "units": "fmwn", "value": 725227}, 
      {"name": "compressor", "tag": "rfs", "units": "imjl", "value": 730777}, 
      {"name": "compressor", "tag": "ohy", "units": "tnbo", "value": 642758}
     ], 
    "schedule_date": "2019-09-13 T 10:21:51", 
    "message_ids": "20190913102151.138@391000176"}

I would expect for the first dictionary to have values assigned just like the following dictionaries that are contained within the 'trend_values' list.

Upvotes: 1

Views: 63

Answers (3)

blhsing
blhsing

Reputation: 106553

The first sub-dict with null values in the sub-list of trend_values is loaded from your existing JSON file with json.load(filename). You can modify that file so that the value of trend_values (and presumably message_ids) is simply an empty sub-list:

{
  "machine_id": null,
  "trend_values": [],
  "schedule_date": null,
  "message_ids": []
}

Upvotes: 1

kaajavi
kaajavi

Reputation: 560

The logic is correct. You append the values after the first dict in your list. Your list has an initial data. You can try with this:

{
  "machine_id": null,
  "trend_values": [],
  "schedule_date": null,
  "message_ids": [
    null
  ]
}

Or changing your script to:

data['machine_id'] = rand_machine_id
data['trend_values'] = []
for item in data:
   rand_tag = get_machine_tag()
   rand_unit = get_machine_unit()
   rand_int = random.randint(1,1000000)
   data['trend_values'].append(({
    'name' : device_name,
    'tag': rand_tag,
    'units': rand_unit,
    'value': rand_int}))
data['schedule_date'] = date_time
data['message_ids'] = message_id

Upvotes: 1

quamrana
quamrana

Reputation: 39354

You have the option of replacing the list that has the single dict with a new empty list first, like this:

data['machine_id'] = rand_machine_id
data['trend_values'] = []
for item in data:
    # code as above

Upvotes: 1

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