Handling JSON array in Python [duplicate]

Question

I'm trying to work with the following incoming json in a Python script running in an AWS Lambda function. This is coming into Lambda on the usual event object as a dict.

{
    "WirelessDeviceId": "AAAAA-BBBBB-CCCC-DDDD-EEEEEEEEEEE",
    "AddedDeviceDecoderType": "TEST",
    "PayloadData": "Aw==",
    "WirelessMetadata": {
      "LoRaWAN": {
        "ADR": true,
        "Bandwidth": 125,
        "ClassB": false,
        "CodeRate": "4/5",
        "DataRate": "3",
        "DevAddr": "LMNOP123",
        "DevEui": "DPLAMSD010101",
        "FCnt": 42,
        "FOptLen": 1,
        "FPort": 4,
        "Frequency": "905100000",
        "Gateways": [
          {
            "GatewayEui": "ABC123",
            "Rssi": -109,
            "Snr": 8
          }
        ],
        "MIC": "ABC900000",
        "MType": "UnconfirmedDataUp",
        "Major": "LoRaWANR1",
        "Modulation": "LORA",
        "PolarizationInversion": false,
        "SpreadingFactor": 7,
        "Timestamp": "2021-08-08T16:04:10Z"
      }
    }
  }

I'm struggling with the "Gateways" array, which may have anywhere from 1 to 10 entries.

Right now, during testing I only have one gateway, and am addressing it in Python like this.

rssi = event['WirelessMetadata']['WirelessMetadata']['Gateways'][0]['Rssi']

But when new gateways are added, I won't know how many Gateways will be inside that array, nor will I know what index they are assigned to so very quickly hard-coding the [0] will not work.

Newbie question, but what is the best way to handle that case? I thought it might have something to do with looping through the array, but I struggled a bit to understand best practice.

Getaway is a a list of dict, so you can retrieve the list and iterate on it. — Yoav Ben Haim
– Yoav Ben Haim, Commented Aug 12, 2021 at 9:51
for gw in event['WirelessMetadata']['WirelessMetadata']['Gateways']: do something with gw — tripleee
– tripleee, Commented Aug 12, 2021 at 9:54

Axisnix · Accepted Answer · 2021-08-12 09:54:49Z

1

You can iterate through the list of gateways.

gateways = event['WirelessMetadata']['WirelessMetadata']['Gateways']

amount_of_gateways = len(gateways)

for gateway in gateways:
    print(gateway["Rssi"])

answered Aug 12, 2021 at 9:54

Axisnix

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