title: How to change values from one column to another in a dataframe using python
body: <p>1- This is my Dataframe</p>
  <pre><code>Date        Open        Buy_Entry   Sell_Entry
  2015-08-31  49.419998   np.nan      np.nan
  2015-09-01  48.110001   np.nan      np.nan
  2015-09-02  48.660000   np.nan      np.nan
  2015-09-03  49.840000   np.nan      np.nan
  2015-09-04  48.810001   np.nan      np.nan
  ... ... ... ...
  2020-09-14  17.940001   np.nan      np.nan
  2020-09-15  17.200001   Buy Entry   np.nan
  2020-09-16  16.100000   Buy Entry   np.nan
  2020-09-17  15.800000   np.nan      np.nan
  2020-09-18  15.960000   np.nan      np.nan
  1273 rows × 3 columns
  </code></pre>
  <p>2- Now, I need to convert into something like this:</p>
  <pre><code>Date        Open        Buy_Entry   Sell_Entry
  2015-08-31  49.419998   np.nan      np.nan
  2015-09-01  48.110001   np.nan      np.nan
  2015-09-02  48.660000   np.nan      np.nan
  2015-09-03  49.840000   np.nan      np.nan
  2015-09-04  48.810001   np.nan      np.nan
  ... ... ... ...
  2020-09-14  17.940001   np.nan      np.nan
  2020-09-15  17.200001   17.200001   np.nan
  2020-09-16  16.100000   16.100000   np.nan
  2020-09-17  15.800000   np.nan      np.nan
  2020-09-18  15.960000   np.nan      np.nan
  1273 rows × 3 columns
  </code></pre>
  <p>I have no problem to replace the np.nan values to 0, but those &quot;Buy Entry&quot; are neccesary to be replaced
  with the &quot;Open&quot; value in that exactly point (index)</p>
  <p>Anny suggestion ?</p>
  <p>I appreciate your help guys. regards!</p>