LykosAI/StabilityMatrix · error · MissingPrerequisiteException

Python was not found and/or failed to install. Please check…

Error message

Python {pyVersion} was not found and/or failed to install. Please check the logs for more details.

What it means

InstallPackageRequirements calls EnsurePythonVersion(pyVersion) to download/install the required Python build; when that returns false (download, hash, or extraction failed) it raises MissingPrerequisiteException for the 'Python' prerequisite, telling the user to check logs. It aggregates any underlying install failure into a single user-facing prerequisite error.

Solutions

1. Check Stability Matrix logs (Help > Open Logs) for the underlying download/hash/extract failure and retry after fixing connectivity.
2. Verify network access to the Python download URL (VPN/proxy/firewall) and retry the package install.
3. If the requested version isn't supported, change the package venv to Python 3.10.11.
4. Clear the partially downloaded python tar.gz under the Assets dir and reinstall.

// pre-check network access to the Python asset host before install
using var ping = new HttpClient();
var resp = await ping.GetAsync(assetUrl, HttpCompletionOption.ResponseHeadersRead);
if (!resp.IsSuccessStatusCode || resp.Content.Headers.ContentLength is null or 0)
    throw new Exception("Python asset unreachable; fix network before install");

try { await helper.InstallPackageRequirements(package, pyVersion, ct); }
catch (MissingPrerequisiteException ex)
{ logger.Error(ex, "Python prerequisite missing; see inner logs"); NotifyUserToCheckLogs(); }

When it happens

Trigger: Installing a package on Unix whose required Python version fails to download, fails SHA-256 verification, fails to extract, or has no bundled asset — EnsurePythonVersion returns false and this exception is thrown.

Common situations: Network failures or proxies blocking the Python tar.gz download; CDN/host serving an HTML error page (hash mismatch); missing asset for non-3.10.11 versions; corrupted archive from a partial download.

Understand the failure class

Background: "not installed", "pip install", "required for": how missing-dependency errors surface across open-source libraries — this error's family across 34 libraries.

Related errors

• Unsupported Python version
• Python download did not contain expected inner 'python'…
• Python download hash mismatch: expected , actual
• Git installation canceled
• Torch is not installed in the virtual environment.

AI-assisted analysis of LykosAI/StabilityMatrix@af93d6ef57 (2026-09-12). Data as JSON: /api/errors/2be55680b39d217d. Report an issue: GitHub.

Appendix: source

Thrown at StabilityMatrix.Avalonia/Helpers/UnixPrerequisiteHelper.cs:146

        List<PackagePrerequisite> prerequisites,
        PyVersion? pyVersion = null,
        IProgress<ProgressReport>? progress = null
    )
    {
        await UnpackResourcesIfNecessary(progress);
        await InstallUvIfNecessary(progress);

        if (prerequisites.Contains(PackagePrerequisite.Python310))
        {
            await InstallPythonIfNecessary(PyInstallationManager.Python_3_10_11, progress);
            await InstallVirtualenvIfNecessary(PyInstallationManager.Python_3_10_11, progress);
        }

        if (pyVersion is not null)
        {
            if (!await EnsurePythonVersion(pyVersion.Value))
            {
                throw new MissingPrerequisiteException(
                    @"Python",
                    @$"Python {pyVersion} was not found and/or failed to install. Please check the logs for more details."
                );
            }
        }

        if (prerequisites.Contains(PackagePrerequisite.Git))
        {
            await InstallGitIfNecessary(progress);
        }

        if (prerequisites.Contains(PackagePrerequisite.Node))
        {
            await InstallNodeIfNecessary(progress);
        }

        if (prerequisites.Contains(PackagePrerequisite.Dotnet))
        {

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