title: Is there a way to add multiple elements in one line to a python set?
body: <p>I am iterating over a pandas dataframe and would like to add unique elements to a set from multiple columns of the dataframe. Currently I do it like this:</p>
  
  <pre><code>list_a = set([])
  for i, row in df.iterrows():
      list_a.add(row.a)
      list_a.add(row.b)
  </code></pre>
  
  <p>I tried this:</p>
  
  <pre><code>list_a = set([])
  for i, row in df.iterrows():
      list_a.add(row.a, row.b)
  </code></pre>
  
  <p>But it results in the following error message: </p>
  
  <pre><code>TypeError: add() takes exactly one argument (2 given)
  </code></pre>
  
  <p>Is there a more elegant way to do this operation than the way I did it (consider the case when there are more than 2 columns to add values from)?</p>