python: ./Include/internal/pycore_stackref.h:99: _PyStackRef_FromPyObjectSteal: Assertion `obj != NULL' failed.
Aborted

from threading import Thread
from collections import ChainMap, Counter
counter = Counter(range(100))
chainmap = ChainMap(counter)
chainmap2 = ChainMap(counter)
def mutate_removing():
    for x in range(10):
        chainmap.pop(list(chainmap.keys()).pop())
        chainmap2.pop(list(chainmap2.keys()).pop())
def mutate_adding():
    for x in range(50):
        chainmap[max(chainmap) + x + 1] = x
        chainmap2[max(chainmap2) + x + 1] = x
alive = []
for x in range(55):
    alive.append(Thread(target=mutate_removing, args=()))
    alive.append(Thread(target=mutate_adding, args=()))
for obj in alive:
    try:
        print('START', obj)
        obj.start()
    except Exception:
        pass