func stringEscape(a py.String) string {
    s := string(a)
    var out bytes.Buffer
    for _, c := range s {
        switch {
        case c < 0x20:
            switch c {
            case '\t':
                out.WriteString(`\t`)
            case '\n':
                out.WriteString(`\n`)
            case '\r':
                out.WriteString(`\r`)
            default:
                out.WriteRune(c)
            }
        case c < 0x100:
            out.WriteRune(c)
        case c < 0x10000:
            fmt.Fprintf(&out, "\\u%04x", c)
        default:
            fmt.Fprintf(&out, "\\U%08x", c)
        }
    }
    return out.String()
}