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Difficulty: HardInterpreting JSON Encoded Data

A Python network automation script stores the following JSON response from a Cisco Catalyst Center API in a dictionary variable named `data`:

{
"response": [
{
"siteId": "USA-NY-OFFICE",
"devices": [
{
"hostname": "Core-Rtr-01",
"managementIp": "192.168.1.1",
"upTimeSeconds": 86400,
"isReachabilityHealthy": true,
"modules": [
{"slot": 0, "status": "OK", "serialNumber": "FOC12345678"},
{"slot": 1, "status": "FAIL", "serialNumber": "FOC87654321"}
]
},
{
"hostname": "Dist-Sw-01",
"managementIp": "192.168.1.2",
"upTimeSeconds": 43200,
"isReachabilityHealthy": false,
"modules": [
{"slot": 0, "status": "OK", "serialNumber": "FOC11223344"}
]
}
]
}
]
}

Which Python expression correctly retrieves the serial number of the failed module on `Core-Rtr-01`, and what is the data type of the returned value?

  1. data["response"][0]["devices"][0]["modules"][1]["serialNumber"] returning a stringAnswer
  2. B
    data["response"][1]["devices"][1]["modules"][2]["serialNumber"] returning a string
  3. C
    data["response"][0]["devices"][0]["modules"][1]["serialNumber"] returning an integer
  4. D
    data["response"]["devices"][0]["modules"][1]["serialNumber"] returning a string

Answer

The expression `data["response"][0]["devices"][0]["modules"][1]["serialNumber"]` correctly retrieves the string value `"FOC87654321"`.
The key `"response"` maps to a list whose first element is at index `0`. Within that dictionary, `"devices"` contains a list where `Core-Rtr-01` is at index `0`. Inside that object, `"modules"` is a list containing the failed module as its second element (index `1`). Accessing `"serialNumber"` extracts `"FOC87654321"`, which is enclosed in double quotes and parsed as a string.

Step-by-Step Solution

1
Examine the top-level structure of the JSON payload.
The top-level structure is a dictionary where key `"response"` maps to a JSON array `[...]`. The array contains a single dictionary at index `0`.
Accessing elements inside the top-level array requires `data["response"][0]`.
2
Locate the target device within the `"devices"` array.
The `"devices"` key maps to a list. `Core-Rtr-01` is the first element, situated at index `0`.
Python list indices start at `0` (`["devices"][0]`).
3
Locate the failed module within the `"modules"` list.
The `"modules"` array for `Core-Rtr-01` contains two dictionary items. Slot 0 is at index `0` and slot 1 (status `"FAIL"`) is at index `1`.
The second element in a zero-indexed list is index `1` (`["modules"][1]`).
4
Extract the key and determine the Python data type.
Accessing key `"serialNumber"` yields `"FOC87654321"`. Surrounding double quotes signify a string data type (`str`).
Quoted literal values in JSON map directly to string types in Python.

Key Concept

Interpreting nested JSON arrays versus objects and mapping JSON values to Python data types.
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Topics

Interpreting JSON Encoded Data

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