Returns the UTF-8 encoded prompt string.

def prompt(self):
        """Returns the UTF-8 encoded prompt string."""
        if self.prompt_string is not None:
            return self.prompt_string

        if not self.color_enabled:
            return (' '.join(self.command) + '>> ').encode('utf8')

        color = '34'
        sub_color = '37'

        prompt_cmd = [
            self.colorize('1;' + color, part) if part != self.cmd_sub_str else
            self.colorize('0;' + sub_color, u'\u2026') for part in self.command
        ]

        return ' '.join(prompt_cmd) + self.colorize('0;' + color, '>> ')