def escape_b(s, quote=True):
    """Replace special characters "&", "<" and ">" to HTML-safe sequences.
    If the optional flag quote is true, the quotation mark character (")
    is also translated."""
    s = s.replace(b'&', b'&amp;')
    s = s.replace(b'<', b'&lt;')
    s = s.replace(b'>', b'&gt;')
    if quote:
        s = s.replace(b'"', b'&quot;')
    return s
