title: df.sort_values is not sorting table (python/pandas)
body: <p>df.sort_values in pandas is not working for me, the same df is getting returned without being sorted.</p>
  
  <pre><code>def findExpression(transType, sortColName=None):
      global df
  
      if transType == 'sortAscending':
          df.sort_values(sortColName)
          return df
  
  print(findExpression('sortAscending', sortColName='col9'))
  
  Actual Output:
      col1  col2        col3        col4      col5  col6   col7   col8  col9
  0  12345  12ab  2008-11-22  2009-11-22     beans  25.0  715.0   True    10
  1  67890  34cd  2009-12-23  2010-12-23  catzilla  25.0   75.0  False     6
  2  13579  56ef  2010-01-24  2011-01-24     boots  25.0   75.0   True     5
  3  24680  78gh  2011-02-25  2012-02-25   whitish  25.0   75.0   True     6
  4  12560  90ij  2012-03-26  2013-03-26      coco  25.0   75.0   True     1
  
  Expected:
      col1  col2        col3        col4      col5  col6   col7   col8  col9
  0  12560  90ij  2012-03-26  2013-03-26      coco  25.0   75.0   True     1
  1  13579  56ef  2010-01-24  2011-01-24     boots  25.0   75.0   True     5
  2  24680  78gh  2011-02-25  2012-02-25   whitish  25.0   75.0   True     6
  3  67890  34cd  2009-12-23  2010-12-23  catzilla  25.0   75.0  False     6
  4  12345  12ab  2008-11-22  2009-11-22     beans  25.0  715.0   True    10
  </code></pre>