Table of Contents

Tooling Support for Python

GraalVM’s Python runtime is incomplete and cannot launch the standard Python debugger pdb. However, it can run the tools that GraalVM provides. The graalpython --help:tools command will give you more information about tools currently supported on Python.


To enable debugging, pass the --inspect option to the graalpython launcher. For example:

graalpython --inspect -c "breakpoint(); import os; os.exit()"
Debugger listening on port 9229.
To start debugging, open the following URL in Chrome:

The standard Python built-in breakpoint() will work using the GraalVM’s Chrome Inspector implementation. You can inspect variables, set watch expressions, interactively evaluate code snippets, etc. However, this only works if you pass --inspect or some other inspect option. Otherwise, pdb is triggered as on CPython (and does not currently work).

Code Coverage

GraalVM comes with a coverage instrument that can be used with --coverage. Use the graalpython --help:tools command to see details on how to use it.

In order to work better with existing Python code, the standard library trace module is partially supported with this low-overhead GraalVM coverage instrument. So you can do this:

graalpython -m trace -m -c -s

This will work similarly to how it would run on CPython.

The programmatic API also works, with some limitations. For example, it does not currently track calls, only line counts and called functions.


The _lsprof built-in module has been implemented using the GraalVM cpusampler tool. Not all profiling features are currently supported, but basic profiling works:

graalpython -m cProfile -s sort -m ginstall --help

The interactive exploration of a stats output file also works:

graalpython -m cProfile -o ginstall.profile -m ginstall --help
graalpython -m pstats ginstall.profile