Indirectlty convert string to float in JSON file

[buran]

don't open it in r+ mode. first open it for reading. After you process data, open it again for writing and dump data.
There are some redundant steps in what you do, e.g. no need to delete the coordinates node first

import json

json_file = 'features.json'

with open(json_file) as f:
    json_data = json.load(f)
    for feature in json_data['features']:
        coordinates = feature['geometry']['coordinates'][0].split(',')
        feature['geometry']['coordinates'] = [float(coord.strip()) for coord in coordinates]

with open(json_file, 'w') as f:
    json.dump(json_data, f, indent=4)