Converting KML files for use with Python library Shapely

Shapely deals with geometric objects, not features or collections of features. See the manual on shape().

Your code (with JSON) could be:

import json
from shapely.geometry import shape
f = open('wijken.json', 'r')
js = json.load(f)
f.close()

for f in js['features']:    
    s = shape(f['geometry'])
    ...