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.
preprocessed = True
        attachments = None
        for atype in (SassStylesheetAsset, LessStylesheetAsset):
            outdated = False
            assets = dict((asset.html_url, asset) for asset in self.stylesheets if isinstance(asset, atype))
            if assets:
                assets_domain = [('url', 'in', list(assets.keys()))]
                attachments = self.env['ir.attachment'].sudo().search(assets_domain)
                for attachment in attachments:
                    asset = assets[attachment.url]
                    if asset.last_modified > fields.Datetime.from_string(attachment['__last_update']):
                        outdated = True
                        break
                    if asset._content is None:
                        asset._content = attachment.datas and base64.b64decode(attachment.datas).decode('utf8') or ''
                        if not asset._content and attachment.file_size > 0:
                            asset._content = None 
                if any(asset._content is None for asset in assets.values()):
                    outdated = True
                if outdated:
                    preprocessed = False
        return preprocessed, attachments
    def preprocess_css(self, debug=False, old_attachments=None):