Append element to json dict (geojson) using Python

I would like to add style to my geojson through Python. The current features currently do not have any style elements. I want to append style and then fill. However, when I do, nothing is added to the file. It is the same as before

import json

with open('test.json') as f:
    data = json.load(f)

for feature in data['features']:
    feature.append("style")
    feature["style"].append({"fill":color})

Sample GeoJson

{
"type": "FeatureCollection",
"crs": { "type": "name", "properties": { "name": "urn:ogc:def:crs:OGC:1.3:CRS84" } },

"features": [
{ "type": "Feature", "properties": { "STATEFP": "17", "COUNTYFP": "019", "TRACTCE": "005401", "BLKGRPCE": "2", "GEOID": "170190054012", "NAMELSAD": "Block Group 2", "MTFCC": "G5030", "FUNCSTAT": "S", "ALAND": 574246.000000, "AWATER": 4116.000000, "INTPTLAT": "+40.1238204", "INTPTLON": "-088.2038105", "GISJOIN": "G17001900054012", "STUSPS": "IL", "SHAPE_AREA": 578361.706954, "SHAPE_LEN": 3489.996273, "census_block_income_YEAR": "2009-2013", "census_block_income_STATE": "Illinois", "census_block_income_STATEA": 17, "census_block_income_COUNTY": "Champaign County"}}]}

I'm trying to get the end results to be:

    {
"type": "FeatureCollection",
"crs": { "type": "name", "properties": { "name": "urn:ogc:def:crs:OGC:1.3:CRS84" } },

"features": [
{ "type": "Feature", "properties": { "STATEFP": "17", "COUNTYFP": "019", "TRACTCE": "005401", "BLKGRPCE": "2", "GEOID": "170190054012", "NAMELSAD": "Block Group 2", "MTFCC": "G5030", "FUNCSTAT": "S", "ALAND": 574246.000000, "AWATER": 4116.000000, "INTPTLAT": "+40.1238204", "INTPTLON": "-088.2038105", "GISJOIN": "G17001900054012", "STUSPS": "IL", "SHAPE_AREA": 578361.706954, "SHAPE_LEN": 3489.996273, "census_block_income_YEAR": "2009-2013", "census_block_income_STATE": "Illinois", "census_block_income_STATEA": 17, "census_block_income_COUNTY": "Champaign County"},"style"{fill:"red"}}]}

Solution

When you type

for feature in data['features']:

every feature will be an item of the list that is data['features']. Each item there is a dictionary, so you are calling the wrong method (append is a method of lists).

You could write

for feature in data['features']:
    feature.update({"style": {"fill": "red"}})

Finally, if you want the file from which you got the initial json structure to be altered, make sure to write the now updated data structure back to a file:

with open('output2.json', 'w') as f:
    json.dump(data, f)