At the moment, "_created" series can be disabled by setting PROMETHEUS_DISABLE_CREATED_SERIES environment variable. If one wants to set it from python, he needs to do it before importing prometheus_client, because the value is calculated on import.
Like this:

os.environ['PROMETHEUS_DISABLE_CREATED_SERIES'] = 'true'
import prometheus_client

That is not very pythonic, style checkers complain on imports not being at top of the file, etc.

Please add an ability to set this option from code, from function call, of just make _use_created variable in metrics.py public.