title: how to convert instance of class "filter" to str directly
body: <pre><code>url = 'https://www.shanbay.com/read/article/97936/' 
  temp = filter(str.isdigit,url)    #slect numbers
  </code></pre>
  
  <p>Instead of using <code>for...in expression</code>, can I convert <code>temp</code> to <code>str</code> directly? </p>