labels method lead to memory leak

I find metrics in my celery task will lead to memory leak. And I reproduced this problem issue locally.

import tracemalloc
from prometheus_client import Counter

counter_a = Counter('request_count_a', 'request count to a', ['name'])
counter_b = Counter('request_count_b', 'request count to b')

tracemalloc.start()
for _ in range(10):
    counter_a.labels('a').inc()
    curr_mem, peak_mem = tracemalloc.get_traced_memory()
    print(f"curr mem: {curr_mem / 10**3} Kb, peak mem: {peak_mem / 10**3} Kb")

print("*****************************************")

for _ in range(10):
    counter_b.inc()
    curr_mem, peak_mem = tracemalloc.get_traced_memory()
    print(f"curr mem: {curr_mem / 10 ** 3} Kb, peak mem: {peak_mem / 10 ** 3} Kb")

It seems to be caused by the labels method. PS: prometheus-client==0.17.1

Start with the provided tracemalloc reproduction and inspect the labels method used by counter_a, comparing it with counter_b.inc(). Confirm whether repeated labels calls cause the reported memory growth, then verify that the reproduced leak is resolved without changing normal counter behavior.