Metadata

Key-value metadata can be attached to each measurement (e.g. run id, tags). It is stored on the Measurement and can be read or mutated for that run.

Supplying metadata

Provide a dictionary when instantiating the Timer:

with Timer(metadata={"run_id": "abc", "tag": "ingest"}) as m:
    do_work()

# m.metadata is {"run_id": "abc", "tag": "ingest"}

Each measurement receives a deep copy of this dictionary at enter time. The Timer retains the original by reference but does not reuse the same dict for multiple measurements.

Per-measurement copy; isolation between runs

• Each block or call receives its own copy of the initial metadata. Mutating measurement.metadata inside that block (or in on_start for that measurement) affects only that measurement.
• If you reuse the same Timer for a second block, the second block’s measurement starts from a fresh deep copy of the Timer’s initial metadata. It does not inherit any keys or changes from the first block.

Mutating metadata

You can mutate measurement.metadata inside the timed block or in on_start to add or change entries for that run (e.g. request id from context, or a tag set after checking a condition). For patterns such as adding a request id in on_start, see Use metadata effectively.