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.

In summary: metadata is scoped to the measurement. Use it to tag that run; it does not leak to the next run.

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.

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