title: What is the explicit python3 type for dict_keys for isinstance() check?
body: <p>In Python3, what type should I use to check if the dictionary keys belong to it?</p>
  
  <pre><code>&gt;&gt;&gt; d = {1 : 2}
  &gt;&gt;&gt; type(d.keys())
  &lt;class 'dict_keys'&gt;
  </code></pre>
  
  <p>So naturally I tried this:</p>
  
  <pre><code>&gt;&gt;&gt; isinstance(d.keys(), dict_keys)
  Traceback (most recent call last):
    File "&lt;stdin&gt;", line 1, in &lt;module&gt;
  NameError: name 'dict_keys' is not defined
  </code></pre>
  
  <p>What should I put in place of the explicit <code>dict_keys</code> as 2nd argument for <code>isinstance</code>? </p>
  
  <p>(This is useful as I have to handle unknown input variables that can take the form of dictionary keys. And I know using <code>list(d.keys())</code> can convert to a list (recovering Python2 behavior) but that's not an option in this case.)</p>