LykosAI/StabilityMatrix · error · InvalidDataException

pyvenv.cfg is UTF-16 encoded; expected UTF-8/ASCII

Error message

pyvenv.cfg is UTF-16 encoded; expected UTF-8/ASCII: {path}

What it means

PyVenvCfg.Load reads a venv's pyvenv.cfg as bytes and rejects files with a UTF-16 BOM (FF FE / FE FF), since venv config must be UTF-8/ASCII. Reading a UTF-16 file as UTF-8 would produce garbage key/value pairs, so an InvalidDataException naming the path is thrown instead.

Solutions

1. Rewrite pyvenv.cfg as UTF-8 (no BOM) using a text editor or 'Set-Content -Encoding utf8NoBOM'
2. Recreate the venv so the config is generated with the correct encoding
3. Convert the file: read as Unicode, write back as UTF-8 before loading
4. Catch InvalidDataException and regenerate the config programmatically

Example fix

// before
powershell: "home = ..." | Set-Content pyvenv.cfg  # UTF-16 by default
// after
powershell: "home = ..." | Set-Content -Encoding utf8NoBOM pyvenv.cfg

var bytes = File.ReadAllBytes(cfgPath);
bool isUtf16 = bytes.Length >= 2 && ((bytes[0] == 0xFF && bytes[1] == 0xFE) || (bytes[0] == 0xFE && bytes[1] == 0xFF));
if (isUtf16) { /* convert to UTF-8 before loading */ }

static bool IsUtf8Clean(string path)
{
    var b = File.ReadAllBytes(path);
    if (b.Length >= 2 && ((b[0] == 0xFF && b[1] == 0xFE) || (b[0] == 0xFE && b[1] == 0xFF))) return false;
    return !new UTF8Encoding(false).GetString(b).Contains('\0');
}

try
{
    var cfg = PyVenvCfg.Load(cfgPath);
}
catch (InvalidDataException ex)
{
    logger.LogWarning(ex, "pyvenv.cfg bad encoding; regenerating");
    RewriteAsUtf8(cfgPath);
    var cfg = PyVenvCfg.Load(cfgPath);
}

When it happens

Trigger: Calling PyVenvCfg.Load on a pyvenv.cfg that was saved as UTF-16 LE/BE — e.g. created by PowerShell 5.x ('>' redirection) or Notepad with 'Unicode' encoding.

Common situations: Windows tooling or scripts rewriting pyvenv.cfg with UTF-16 default encoding; a venv created/patched by a PowerShell script that out-recreated the config.

Related errors

• pyvenv.cfg contains NUL bytes; expected UTF-8/ASCII
• Torch is not installed in the virtual environment.
• ComfyUI venv was not found at
• Windows ROCm bitsandbytes is only supported on Python 3.12.x
• Failed to start Forge Classic install process

AI-assisted analysis of LykosAI/StabilityMatrix@af93d6ef57 (2026-09-12). Data as JSON: /api/errors/0345c9231b4a1efc. Report an issue: GitHub.

Appendix: source

Thrown at StabilityMatrix.Core/Python/PyVenvCfg.cs:63

        return new PyVenvCfg(entries);
    }

    /// <summary>
    /// Loads a pyvenv.cfg file. Fails loudly on non-UTF-8 encodings instead of
    /// silently mangling the file.
    /// </summary>
    public static PyVenvCfg Load(string path)
    {
        var bytes = File.ReadAllBytes(path);

        // pyvenv.cfg is UTF-8/ASCII; reject UTF-16 BOMs and NUL bytes, which
        // indicate the file was read with the wrong encoding.
        if (
            bytes.Length >= 2
            && ((bytes[0] == 0xFF && bytes[1] == 0xFE) || (bytes[0] == 0xFE && bytes[1] == 0xFF))
        )
        {
            throw new InvalidDataException($"pyvenv.cfg is UTF-16 encoded; expected UTF-8/ASCII: {path}");
        }

        var content = new UTF8Encoding(false).GetString(bytes);
        if (content.Contains('\0'))
        {
            throw new InvalidDataException($"pyvenv.cfg contains NUL bytes; expected UTF-8/ASCII: {path}");
        }

        return Parse(content);
    }

    /// <summary>
    /// Gets the value of the last matching key (CPython is last-wins), or null.
    /// Setting rewrites every matching key, appending a new key when absent.
    /// </summary>
    public string? this[string key]
    {
        get

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