only_polygons.py

#!/usr/bin/env python
'''Removes all non-polygon features from a GeoJSON file.

For now, these must be FeatureCollections of Features.
'''

import sys
import json

assert len(sys.argv) == 2
d = json.load(file(sys.argv[1]))

assert d['type'] == 'FeatureCollection'

indices_to_delete = []
for idx, feat in enumerate(d['features']):
    assert feat['type'] == 'Feature'
    if feat['geometry']['type'] not in ['Polygon', 'MultiPolygon']:
        indices_to_delete.append(idx)

for idx in reversed(indices_to_delete):
    del d['features'][idx]

print json.dumps(d, indent=2)