title: Adding a column in pandas df using a function
body: <p>I have a Pandas df [see below].
  How do I add values from a function to a new column "price"?</p>
  
  <pre><code>function:
  
      def getquotetoday(symbol):
          yahoo = Share(symbol)
          return yahoo.get_prev_close()
  
  df:
  
  Symbol    Bid      Ask
  MSFT     10.25   11.15
  AAPL     100.01  102.54
  
  
    (...)
  </code></pre>