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.
self.stylesheets.insert(0, StylesheetAsset(self, inline=at_rules))
                while fragments:
                    asset_id = fragments.pop(0)
                    asset = next(asset for asset in self.stylesheets if asset.id == asset_id)
                    asset._content = fragments.pop(0)
                    if debug:
                        try:
                            fname = os.path.basename(asset.url)
                            url = asset.html_url
                            with self.env.cr.savepoint():
                                self.env['ir.attachment'].sudo().create(dict(
                                    datas=base64.b64encode(asset.content.encode('utf8')),
                                    mimetype='text/css',
                                    type='binary',
                                    name=url,
                                    url=url,
                                    datas_fname=fname,
                                    res_model=False,
                                    res_id=False,
                                ))
                            if self.env.context.get('commit_assetsbundle') is True:
                                self.env.cr.commit()
                        except psycopg2.Error:
                            pass
        return '\n'.join(asset.minify() for asset in self.stylesheets)
    def compile_css(self, cmd, source):
        """Sanitizes @import rules, remove duplicates @import rules, then compile"""
        imports = []
        def sanitize(matchobj):