title: Pandas concatenate all members of a column with a constant string
body: <p>So I am trying to take all of the members of a Pandas Dataframe Column and add the string <code>EQUITY</code>
  to them (there is a space before equity). Right now this is what I have:</p>
  
  <pre><code>response_score_factors["ULT_PARENT_TICKER_EXCHANGE"] = response_score_factors["ULT_PARENT_TICKER_EXCHANGE"].str.cat(" EQUITY")
  </code></pre>
  
  <p>This is the error I am getting:
      raise ValueError("Did you mean to supply a <code>sep</code> keyword?")
  ValueError: Did you mean to supply a <code>sep</code> keyword? To my knowledge sep would not concatenate the last string so I am not using that. Any ideas? Thanks!</p>