title: Where is documentation on set's class methods?
body: <p>I gather from answers like <a href="https://stackoverflow.com/a/2541814/1393162">this</a> that Python's built-in type <code>set</code> has a number of useful class methods, such as <code>set.intersection()</code>. Where are they documented? I haven't found them documented <a href="https://docs.python.org/3.7/library/stdtypes.html#set" rel="nofollow noreferrer">here</a>, which seems to cover only the instance methods.</p>
  
  <p>Here's an example demonstrating the existence of one of these class methods:</p>
  
  <pre><code>&gt;&gt;&gt; set.intersection(set([1, 2, 3]), set([2, 3, 4]))
  {2, 3}
  
  &gt;&gt;&gt; set.intersection([1, 2, 3], [2, 3, 4])
  Traceback (most recent call last):
    File "&lt;stdin&gt;", line 1, in &lt;module&gt;
  
  &gt;&gt;&gt; set([1, 2, 3, 4]).intersection([1, 2, 3], [2, 3, 4])  # same args, passed to instance method
  {2, 3}
  </code></pre>
  
  <p>The <a href="https://docs.python.org/3.7/library/stdtypes.html#frozenset.intersection" rel="nofollow noreferrer">documentation for the instance method</a> says that it accepts any iterable as an argument, not just a set. The example above shows that the class method works differently.</p>
  
  <p>It would be nice to know what arguments you are supposed to be able to pass to these functions without having to guess and test.</p>