Attributes for the update.

For performance reasons, this is the same object across updates for the same attribute set. This means py`id` will be the same for the same attribute set across updates. Note this is for same "attribute set" as created by the metric creator, but different attribute sets may have the same values.

Do not mutate this.

Metric being updated.

For performance reasons, this is the same object across updates for the same metric. This means py`id` will be the same for the same metric across updates.

Value for the update.

For counters this is a delta, for gauges and histograms this is just the value.