LykosAI/StabilityMatrix · error · ProcessException

pip show returned no output for package

Error message

pip show returned no output for package '{packageName}': {result.StandardError}

What it means

UvVenvRunner.PipShow throws this ProcessException when `uv pip show` exits successfully (code 0) but StandardOutput is empty or whitespace, so PipShowResult.Parse would have nothing to parse. The package-not-found case is handled separately (returns null), so an empty-but-successful result means pip gave an inconsistent/blank response — usually stderr (included in the message) explains why.

Solutions

Check the StandardError text in the exception message for pip's explanation.
Run the same `uv pip show <pkg> --python <venvPython>` command manually to reproduce and inspect raw output.
Update uv to a current version so `pip show` emits standard output.
If the environment is suspect, recreate the venv and retry the query.

Example fix

// before: assuming a null return covers all negative outcomes
var info = await runner.PipShow(pkg);
// after: also handle the empty-output exception
PipShowResult? info;
try { info = await runner.PipShow(pkg); }
catch (ProcessException ex) when (ex.Message.Contains("returned no output")) {
    info = null; // treat as unknown/uninstalled after logging ex.Message
}

Defensive patterns

Strategy: try-catch

Validate before calling

var probe = await ProcessRunner.GetProcessResultAsync(runner.UvExecutablePath, new[] { "--version" }, null, null);
if (probe.ExitCode != 0) throw new InvalidOperationException("uv broken");

Type guard

static bool UvWorks(UvVenvRunner r) => File.Exists(r.UvExecutablePath);

Try / catch

try { info = await runner.PipShow(pkg); }
catch (ProcessException ex) when (ex.Message.Contains("returned no output")) { info = null; }

Prevention

Treat empty stdout with exit 0 as an anomaly; log stderr from the message.
Pin a known-good uv version for reproducible pip output.
Check environment variables passed to the runner don't redirect/suppress output.

When it happens

Trigger: Calling PipShow(packageName) where the subprocess returns exit code 0 but no stdout: pip emitting only errors to stderr while still exiting 0, an unusual uv version suppressing show output, or output redirection/capture producing nothing.

Common situations: Odd uv/pip builds with nonstandard show output; environment (env vars, locale) altering pip behavior; stdout swallowed by a misconfigured ProcessRunner capture; exotic package metadata that makes pip print nothing.

Related errors

AI-assisted analysis of LykosAI/StabilityMatrix@af93d6ef57 (2026-09-12). Data as JSON: /api/errors/c787862d49c4d2c9. Report an issue: GitHub.

Appendix: source

Thrown at StabilityMatrix.Core/Python/UvVenvRunner.cs:401

            || result.StandardError?.Contains("Package(s) not found", StringComparison.OrdinalIgnoreCase)
                == true;

        if (packageNotFound)
        {
            return null;
        }

        // Check return code
        if (result.ExitCode != 0)
        {
            throw new ProcessException(
                $"pip show failed with code {result.ExitCode}: {result.StandardOutput}, {result.StandardError}"
            );
        }

        if (string.IsNullOrWhiteSpace(result.StandardOutput))
        {
            throw new ProcessException(
                $"pip show returned no output for package '{packageName}': {result.StandardError}"
            );
        }

        return PipShowResult.Parse(result.StandardOutput);
    }

    /// <summary>
    /// Run a pip index command, return result as PipIndexResult.
    /// </summary>
    public async Task<PipIndexResult?> PipIndex(
        string packageName,
        string? indexUrl = null,
        bool includePrerelease = false
    )
    {
        if (!File.Exists(PipPath))
        {

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