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.
rx_indent = re.compile(r'^( +|\t+)', re.M)
    indent = None
    reindent = '    '
    def minify(self):
        return self.with_header()
    def get_source(self):
        content = textwrap.dedent(self.inline or self._fetch_content())
        def fix_indent(m):
            
            ind = m.group()
            if self.indent is None:
                self.indent = ind
                if self.indent == self.reindent:
                    
                    raise StopIteration()
            return ind.replace(self.indent, self.reindent)
        try:
            content = self.rx_indent.sub(fix_indent, content)
        except StopIteration:
            pass
        return "/*! %s */\n%s" % (self.id, content)
    def get_command(self):
        try:
            sass = misc.find_in_path('sass')
        except IOError:
            sass = 'sass'
        return [sass, '--stdin', '-t', 'compressed', '--unix-newlines', '--compass',
                '-r', 'bootstrap-sass']
class LessStylesheetAsset(PreprocessedCSS):