class TTFont:
    # ...
    def splitString(self, text, doc, encoding='utf-8'):
        # ...
        cur.append(n & 0xFF) # <-- here is the problem!
        # ...

my_doctemplate.build([Paragraph(bulletText = None, encoding = 'utf8',
    caseSensitive = 1, debug = 0,
    text = 'xd8xa3xd8xa8xd8xb1xd8xa7xd8xac',
    frags = [ParaFrag(fontName = 'DejaVuSansMono-BoldOblique',
        text = 'xd8xa3xd8xa8xd8xb1xd8xa7xd8xac',
        sub = 0, rise = 0, greek = 0, link = None, italic = 0, strike = 0,
        fontSize = 12.0, textColor = Color(0,0,0), super = 0, underline = 0,
        bold = 0)])])