title: how to remove this warning in python 3
body: <p>trying to lower and strip a column in python 3 using panda, but getting the warning-- what is the right way so this warning will not come up </p>
  
  <pre><code>df["col1"] = df[["col1"]].apply(lambda x: x.str.strip())
  df["col1"] = df[["col1"]].apply(lambda x: x.str.lower())
  </code></pre>
  
  <p>The warning</p>
  
  <pre><code>A value is trying to be set on a copy of a slice from a DataFrame.
  Try using .loc[row_indexer,col_indexer] = value instead
  
  See the caveats in the documentation: http://pandas.pydata.org/pandas-docs/stable/indexing.html#indexing-view-versus-copy
    self[k1] = value[k2]
  </code></pre>
  
  <p>how to remove the warning</p>