As in prometheus/client_golang#1369 and prometheus/client_java#916, the Python library needs to be updated to support UTF-8.

Tasks:

• Update exposition format parsers for the new syntax
• Update PromQL parsers (if any) for the new syntax
• Update content negotiation logic
• Add flag to enable change in validation logic to check that metric and label names are UTF-8 valid instead of the old letters/numbers/underscores/colons set

For background and references see prometheus/prometheus#13095