Histogram without label creates histogram_*.db even without data

I tried this with versions: 0.19.0 and 0.20.0, both seem to have this bug.

I have a script prom_example.py:

from prometheus_client import Histogram

Example = Histogram("example", "Example", "lol")

When I run it:

prometheus_multiproc_dir=/tmp/metrics python prom_example.py

I see nothing in /tmp/metrics (as expected).

But when I edit the script and remove the label from histogram:

from prometheus_client import Histogram

Example = Histogram("example", "Example")

Database is created is /tmp/metrics, named for example: histogram_37373.db I would expect no database creation, since no data is pushed into the metric.

Edit: it seems the behaviour is the same for Counter and Gauge

Riproduci il problema con lo script prom_example.py e prometheus_multiproc_dir usando un Histogram senza label, quindi confrontalo con il caso con label. Controlla i percorsi di inizializzazione di Histogram, Counter e Gauge; il lavoro è completato quando non viene creato alcun file .db prima che vengano registrati dati delle metriche.