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
attachments = self.get_attachments('js')
        if not attachments:
            content = ';\n'.join(asset.minify() for asset in self.javascripts)
            return self.save_attachment('js', content)
        return attachments[0]
    def css(self):
        attachments = self.get_attachments('css')