Iterating through a json in python - only wanting the value for one key in multiple dicts-CodePudding

I have this Json file, and I want to get the "navn" out with a iterating. I need it to print: Traktor Bil and nothing else, how do I do that ?

[
    {"navn": "Traktor", "år": 10, "købspris": 10000},
    {"navn": "Bil", "år": 20, "købspris": 100000},
    {},
    {}
    ]

So far I have this idea I know I need to import json file, and iterating through it but every time it gives me a error... I have tried searching the whole wide web and nothing came up my code so far:

import json
def main():
    f = open("/Users/maltheschroderjakobsen/Desktop/coding/test/mat.json",)
    f = json.load(f)
    for key in f["navn"]:
        print (key)    
main()

But every time I try anything else it gives me a error

CodePudding user response：

f seems to be a list, not a dictionary:

for dct in f:
    if "navn" in dct:  # the elements are dicts!
        print(dct["navn"])

CodePudding user response：

It's because some dicts have no key navn. Use dict.get instead:

import json
def main():
    file = open("/Users/maltheschroderjakobsen/Desktop/coding/test/mat.json",)
    data = json.load(file)
    for dct in data:
        print(dct.get("navn", ""))
main()

CodePudding user response：

So long as the JSON only has dicts, you can do:

js='''\
[
    {"navn": "Traktor", "år": 10, "købspris": 10000},
    {"navn": "Bil", "år": 20, "købspris": 100000},
    {},
    {}
]'''
    
import json 

>>> [e['navn'] for e in json.loads(js) if e.get('navn', '')]
['Traktor', 'Bil']

JSON can also have other datatypes such as lists or numeral. If there is a possibility of something other than a dict in the JSON, you can do:

[e['navn'] for e in json.loads(js) if isinstance(e, dict) and e.get('navn', '')]