import overpass
import json

api = overpass.API()

res = api.get("""
    area[name="Florida"];
    rel[name="Sumter County"](area);
    map_to_area;
    (
      nwr[highway~"^(motorway|trunk|primary|secondary|tertiary|residential|unclassified|motorway_link|trunk_link|primary_link|secondary_link|tertiary_link)$"](area);
    );
    (._;>;);
""", responseformat="geojson")

# if you want a str, then use dumps function
#geojson_str = geojson.dumps(res)

# dump as file, if you want to save it in file
with open("./test.geojson",mode="w") as f:
  json.dump(res, f)