Austin VS Code Extension

Profile and analyse your Python application inside VS Code using Austin.

Pre-requisites

This extension requires Austin 3. See Austin for installation instructions for your platform. If you want to compile from sources or use one of the available release binaries, you can specify the absolute location of the Austin binary in the settings.

Usage

There are two ways of executing Austin from VS Code. Either using a configured task, or a one-off execution.

[!NOTE] When using a Python virtual environment, you might need to manually add the path of the Austin binary to the extension settings. You can do so by searching for the austin.path setting and typing the (absolute) path to the binary, e.g. /home/user/project/.venv/bin/austin.

[!NOTE] MacOS users should consider adding a rule for Austin to their sudoers file. This will allow you to run sudo austin ... without having to type your user password. This is required if you want to run Austin through the extension tasks. To add a rule for Austin to the sudoers file, run sudo visudo and add

<USER>        ALL = (root) NOPASSWD: <PATH_TO_AUSTIN>

at the end, replacing <USER> and <PATH_TO_AUSTIN> with your user name and the path to the Austin binary respectively. If you are using environment files in task definitions, you might also need to use the SETENV directive:

<USER>        ALL = (root) NOPASSWD:SETENV: <PATH_TO_AUSTIN>

Profiling with tasks

The Austin extension provides a "austin" task type to VS Code. The VS Code Tasks system is the best way to define jobs to run against your code, like profiling. Create a tasks.json inside the .vscode folder in the root of your workspace:

{
    "version": "2.0.0",
    "tasks": [
        {
            "type": "austin",
            "file": "main.py",
            "label": "Profile main.py",
        }
    ]
}

You can also specify a list of arguments to send to your Python script. This is equivalent of running python main.py --verbose:

{
    "version": "2.0.0",
    "tasks": [
        {
            "type": "austin",
            "file": "main.py",
            "args": ["--verbose"],
            "label": "Profile main.py",
        }
    ]
}

To Run the task, execute Tasks: Run Task from the Command Palette and select the task you specified in tasks.json.

If you need to run a more generic command, for example by invoking a virtual environment manager like Poetry, you can use the command field, e.g.

{
    "version": "2.0.0",
    "tasks": [
        {
            "type": "austin",
            "label": "Profile tests",
            "command": [
                "poetry",
                "run"
            ],
            "args": [
                "python",
                "-m",
                "pytest",
            ]
        }
    ]
}

In the above task definition, the Austin command is placed in between the command and the args lists. That is, the above ends up running

poetry run austin <austin args> python -m pytest

from the current working directory.

Tasks also support the use of the placeholders ${workspaceFolder} and ${file}, and the use of environment files via the envFile property. To make use of the latter on MacOS, you need to use ["sudo", "-E"] for the command property.

Profiling a standalone script

To profile a Python script, open it up in VS Code, open the command palette and search for Profile with Austin, or press Shift + F5. If you already have a file with Austin samples, open the panel, head to the FLAME GRAPH view and click the OPEN button to select the file. Alternatively, once the panel has been revealed, search for the Load Austin samples ... command in the palette, or press Ctrl/Cmd + Shift + A.

The flame graph is interactive and when you click on a frame, the corresponding source will be opened (assuming that all the paths can be resolved correctly) in VS Code and lines highlighted based on the amount of time spent on them.

To search through an open flame graph, press F and type a search string. To reset the view, simply press R. Conveniently, you can bring up the open dialog with O while the focus is on the flame graph panel.

The extension also adds two interactive tree views in the side bar to explore the sampled call stack and the top functions. Click on the Austin logo in the activity bar to reveal them.

Expression-level heat maps

To enable support for column-level location information, ensure that the Austin extension is set up to use the binary mode in the extension settings. Note that this requires at least the version 3.5 of Austin to work. Binary mode itself only requires Austin 3.4 to work. Earlier Austin versions don't support binary mode and the extension won't work if in binary mode.

Configuration

Whenever you have an active Python script, the sampling interval and mode selector will appear on the status bar. Select between wall-clock time and CPU time sampling, and the sampling interval in microseconds.