LykosAI/StabilityMatrix · error · FileNotFoundException

Python installation not found at

Error message

Python {version} installation not found at {installation.InstallPath}

What it means

PyRunner.SwitchToInstallation looks up a Python installation for the requested version via the installation manager and verifies it exists on disk before switching. If the installation directory is missing, a FileNotFoundException is thrown naming the expected InstallPath.

Solutions

  1. Install the required Python version (let the installation manager download/set it up) before switching
  2. Verify installation.InstallPath exists on disk before calling SwitchToInstallation
  3. Use the default installation if an exact version is optional
  4. Catch FileNotFoundException and trigger re-setup of the Python environment

Example fix

// before
await pyRunner.SwitchToInstallation(PyVersion.Parse("3.10.11")); // install deleted
// after
var install = await installationManager.GetInstallationAsync(PyVersion.Parse("3.10.11"));
if (!install.Exists())
    await installationManager.SetupSharedRuntimeAsync(PyVersion.Parse("3.10.11"));
await pyRunner.SwitchToInstallation(PyVersion.Parse("3.10.11"));
Defensive patterns

Strategy: validation

Validate before calling

var installation = await installationManager.GetInstallationAsync(version);
if (!Directory.Exists(installation.InstallPath))
    await installationManager.SetupSharedRuntimeAsync(version);

Try / catch

try
{
    await pyRunner.SwitchToInstallation(version);
}
catch (FileNotFoundException ex)
{
    logger.LogError(ex, "Python {Version} install missing; re-provisioning", version);
    await installationManager.SetupSharedRuntimeAsync(version);
    await pyRunner.SwitchToInstallation(version);
}

Prevention

When it happens

Trigger: Calling SwitchToInstallation(version) when no CPython installation of that version exists at the expected path — e.g. after deleting the venv/python folder, or requesting a version that was never installed.

Common situations: User removed or moved the Python install directory, shared-environment cleanup, a shared install being re-downloaded, requesting an old version after an upgrade.

Understand the failure class

Background: "File not found" and ENOENT errors: why libraries can't find a file that should exist — this error's family across 50 libraries.

Related errors

AI-assisted analysis of LykosAI/StabilityMatrix@af93d6ef57 (2026-09-12). Data as JSON: /api/errors/cb2f360be538f64d. Report an issue: GitHub.

Appendix: source

Thrown at StabilityMatrix.Core/Python/PyRunner.cs:169

                "System.Runtime.Serialization.EnableUnsafeBinaryFormatterSerialization",
                true
            );
            Logger.Info("Shutting down previous Python runtime for version switch");
            PythonEngine.Shutdown();
            AppContext.SetSwitch(
                "System.Runtime.Serialization.EnableUnsafeBinaryFormatterSerialization",
                false
            );
        }

        // If not initialized or we had to shutdown, initialize with the new version
        if (!PythonEngine.IsInitialized)
        {
            // Get the installation for this version
            var installation = await installationManager.GetInstallationAsync(version).ConfigureAwait(false);
            if (!installation.Exists())
            {
                throw new FileNotFoundException(
                    $"Python {version} installation not found at {installation.InstallPath}"
                );
            }

            currentInstallation = installation;

            // Initialize with this installation
            await InitializeWithInstallation(installation).ConfigureAwait(false);
        }
    }

    /// <summary>
    /// Initialize Python runtime with a specific installation
    /// </summary>
    private async Task InitializeWithInstallation(PyInstallation installation)
    {
        if (PythonEngine.IsInitialized)
            return;

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