python io.load memory usage issue

[veekxt]

I found that laneletMap occupies memory for at least one object. In the example below, it doesn't occupy memory for 8 objects, which seems normal. However, it will still occupy memory for one object, which is hard to accept, especially since my OSM file is large. How can I clear all memory usage?

import lanelet2
import time

def build_graph():
    j = lanelet2.projection.UtmProjector(lanelet2.io.Origin(49.0, 8.4))
    lanelet_map = lanelet2.io.load("files/t2.osm", j)
    del lanelet_map # del also doest work
    return None

if __name__ == "__main__":
    for i in range(8):
        build_graph()
    time.sleep(100)

And, a 70MB OSM file that occupies about 600MB of memory. What are the methods to reduce memory usage as much as possible?