According document of 'What’s New In Python 3.7', 'async' are reserved keywords now.

Code in line 105 of 'odoo/addons/base/ir/ir_qweb/assetsbundle.py' 
`def to_html(self, sep=None, css=True, js=True, debug=False, async=False, url_for=(lambda url: url)):`
will throw SyntaxError out if we launch odoo with this update python.
odoo/addons/base/ir/ir_qweb/assetsbundle.py
assert type in ('js', 'css')
        ira = self.env['ir.attachment']
        fname = '%s%s.%s' % (self.name, ('' if inc is None else '.%s' % inc), type)
        mimetype = 'application/javascript' if type == 'js' else 'text/css'
        values = {
            'name': "/web/content/%s" % type,
            'datas_fname': fname,
            'mimetype' : mimetype,
            'res_model': 'ir.ui.view',
            'res_id': False,
            'type': 'binary',
            'public': True,
            'datas': base64.b64encode(content.encode('utf8')),
        }
        attachment = ira.sudo().create(values)
        url = '/web/content/%s-%s/%s' % (attachment.id, self.version, fname)
        values = {
            'name': url,
            'url': url,
        }
        attachment.write(values)
        if self.env.context.get('commit_assetsbundle') is True:
            self.env.cr.commit()
        self.clean_attachments(type)
        return attachment
    def js(self):