title: Pandas Loop through list of Data Frames and Change Index
body: <p>This is a basic quesion, but I want to loop through a list of data frames and for each data frame, set the index as one of the columns in the data frame.  The issue with the code below is that it doesn't save the data frame with a new index.  How do I format this For loop so that the dataframes are permanently changed outside of the for loop? Thanks.</p>
  
  <pre><code>dflist = [df_1, df_2, df_3]
  
  for i in dflist:
      i = i.set_index('column_2')
  </code></pre>