title: How to change the values of only part (slice) of a list of strings
body: <p>Does anyone know how to concatenate a list of strings using a for loop?</p>
  
  <p>This works, without a loop:</p>
  
  <h1>Extract Column Names</h1>
  
  <pre><code>column_names = file.columns.tolist()
  column_names[1]= column_names[1] + '_Vol_Adj'
  column_names[1]
  </code></pre>
  
  <p>But does not work as part of the following loop:</p>
  
  <pre><code>for i in column_names[1:-2]:
      column_names[i]= column_names[i] + '_Vol_Adj'
      i = i+1
  </code></pre>
  
  <blockquote>
  <pre><code>TypeError                                 Traceback (most recent call last)
  &lt;ipython-input-242-5509cede9f32&gt; in &lt;module&gt;()
        2 
        3 for i in column_names[1:-2]:
  ----&gt; 4     column_names[i]= column_names[i] + '_Vol_Adj'
        5     i = i+1
  
  TypeError: list indices must be integers or slices, not str
  </code></pre>
  </blockquote>