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
return """
            (function (message) {
                if (window.__assetsBundleErrorSeen) return;
                window.__assetsBundleErrorSeen = true;
                document.addEventListener("DOMContentLoaded", function () {
                    var alertTimeout = setTimeout(alert.bind(window, message), 0);
                    if (typeof odoo === "undefined") return;
                    odoo.define("AssetsBundle.ErrorMessage", function (require) {
                        "use strict";
                        var base = require("web_editor.base");
                        var core = require("web.core");
                        var Dialog = require("web.Dialog");
                        var _t = core._t;
                        clearTimeout(alertTimeout);
                        base.ready().then(function () {
                            new Dialog(null, {
                                title: _t("Style error"),
                                $content: $("<div/>")
                                    .append($("<p/>", {text: _t("The style compilation failed, see the error below. Your recent actions may be the cause, please try reverting the changes you made.")}))
                                    .append($("<pre/>", {html: message})),
                            }).open();
                        });
                    });
                });
            })("%s");
        """ % message.replace('"', '\\"').replace('\n', '&NewLine;')
    def is_css_preprocessed(self):