title: Pandas: Rename single DataFrame column without knowing column name
body: <p>I know I can rename single pandas.DataFrame columns with:</p>
  
  <pre><code>drugInfo.rename(columns = {'col_1': 'col_1_new_name'}, inplace = True)
  </code></pre>
  
  <p>But I'd like to rename a column without knowing its name (based on its index - although I know dictionaries don't have it). I would like rename column number 1 like this:</p>
  
  <pre><code>drugInfo.rename(columns = {1: 'col_1_new_name'}, inplace = True)
  </code></pre>
  
  <p>But in the DataFrame.columns dict there is no '1' entry, so no renaming is done. How could I achieve this?</p>