How to filter a JSON?

Python Help
#1

Good day community,

Maybe someone could recommend the best way how to filter a JSON output? I’ve made an API request to the server and got a reply:

[
  {
    "Id": 111111,
    "description": [
      {
        "criteria": "Cache",
        "measurement": null,
        "comlexName": null,
        "value": "32MB",
        "criteriaId": 907,
        "valueId": null,
        "comlexId": null,
        "lastUpdateDate": "2021-03-23T11:09:32.293"
      }
    ]
  }
]

How can I get only certain keys? In this example I’m interested in “criteria” and “value”

Thank you in advance :slight_smile:

#2

My rough attempt without testing, using pattern matching


match reply:

     case [{"description": {"criteria": str() as criteria, "value“: str() as value}]:
          print(criteria, value)

That will get you the first criteria and value if you have a list holding a dictionary with key description whose value is a dict with keys criteria and value whose values are str…I think

A better way might be


for entry in reply:
    match entry:
        case {"description": {"criteria": str() as criteria, "value": str() as value}:
            print(criteria, value)
1 Like
#3

I am pretty new to match-case so I was curious which exact form works. Here is the code by @Melendowski made into runnable code (it is not necessary to use the keyword as):

Input data (click to show) 
null = None
reply = [
  {
    "Id": 111111,
    "description": [
      {
        "criteria": "Cache",
        "measurement": null,
        "comlexName": null,
        "value": "32MB",
        "criteriaId": 907,
        "valueId": null,
        "comlexId": null,
        "lastUpdateDate": "2021-03-23T11:09:32.293"
      }
    ]
  }
]

match reply:
     case [
             {"description": [
                 {"criteria": str(criteria), "value": str(value)}
             ]}]:
          print(criteria, value)

Cache 32MB

As John wrote, you would probably want to iterate the the list items in for loops.

2 Likes
#4

Thank you all for your reply!

What if I have multiple blocks, like:

 [{'productId': 1111111, 'description': [
            {
                'criteria': 'Cache',
                'measurement': None,
                'comlexName': None, 
                'value': '32MB', 
                'orderNo': '10', 
                'criteriaId': 907, 
                'valueId': None, 
                'comlexId': None, 
                'lastUpdateDate': '2021-03-23T11:09:32.293'
            }, 
            {
                'criteria': 'Code', 
                'measurement': None, 
                'comlexName': None, 
                'value': 'UPS', 
                'orderNo': '999', 
                'criteriaId': 999, 
                'valueId': None, 
                'comlexId': None, 
                'lastUpdateDate': '0001-01-01T00:00:00'
            },
            {
                'criteria': 'Speed', 
                'measurement': 'MHz', 
                'comlexName': None, 
                'value': '3700', 
                'orderNo': '6', 
                'criteriaId': 906, 
                'valueId': None, 
                'comlexId': None, 
                'lastUpdateDate': '2021-03-23T11:09:32.293'
            } ]}]

I had tried what you suggested, but it didn’t output anything.

#5

That is the correct behaviour. The number of list items in the case pattern must match the number of list items in the data. Demonstration:

test_lists = (
    ['Crusoe'],
    ['Holmes', 'Watson'],
    )

for test_list in test_lists:
    print(f'--- testing {test_list}, all matches:')
    match test_list:
        case [a]:
            print(f'One item list match: {a!r}')
    match test_list:
        case [a, b]:
            print(f'Two items list match: {a!r}, {b!r}')
    print()

--- testing ['Crusoe'], all matches:
One item list match: 'Crusoe'

--- testing ['Holmes', 'Watson'], all matches:
Two items list match: 'Holmes', 'Watson'

So, as John suggested and provided example: iterate the list.

Extract it from your data:

...
     case [{"description": list(descriptions_list)}]:
        ...

…and iterate it using for. In the loop use another match statement to extract the data from the individual items.

1 Like