Frequently asked questions

Which backend should I choose?

Use Trace for exact execution counts, Scalene for sampling or GPU metrics, and Tachyon for sampling on Python 3.15. See backends.

Do I need to edit my script?

Run linescope your_script.py or linescope -m your_package.your_module. Use the profile context manager to measure only part of the program.

Where is time inside pandas or NumPy shown?

Library and I/O work is attributed to the calling project line. Third-party source is hidden. See profiling scope.

Does missing time mean a line never ran?

No. Sampling can miss short lines. A dash means unavailable; samples are observations, not execution counts.

Why can a function have time but no call count?

Profiling may have started inside it, after its entry. Its measured time stays in the report; Calls and Avg / call are unavailable.

How much overhead does profiling add?

Trace can noticeably slow tight loops. Memory tracking and live notebook reports add work too. Compare runs with the same settings and verify gains without the profiler. See performance.

How do I save without opening a report?

Set display="none", then call session.save("report.html"). Reports display inline in notebooks by default and in a browser elsewhere.

Can I profile several notebook cells?

Start with profile.start(), run the cells, then call profile.stop(). See notebook display modes.

What does memory include?

Process RAM includes native buffers and profiler overhead. Retained Python allocations are measured separately; do not add them to RAM. Workers and GPU memory are outside driver RAM. See memory.

Does profiling trigger Spark actions?

No. It observes existing actions. Parallel task time can exceed driver wall time, and executor Python lines are not profiled. See Spark.

Are Databricks child notebooks profiled?

Python children called through dbutils.notebook.run are collected and merged by default. This needs LineScope in the child environment and workspace permissions. See Databricks.

Why are some calls not clickable?

Dynamic dispatch, ambiguous definitions, and third-party calls may not have a resolvable project target. See source navigation.

Can I share a report or open it offline?

Reports embed their source and assets. They work without the original project or a server. Review captured source for private data before sharing.