title: Implementing cdc but getting value error in Python Pandas
body: <p>I am trying to perform CDC operation via Python. I am trying to perform union of the unchanged data (master file / base table) with the new file (delta file).</p>
  
  <p>Below is the function I have written:</p>
  
  <pre><code>def processInputdata():
      df1 = pd.read_csv('master.csv')
      df2 = pd.read_csv('delta.csv')
      df=pd.merge(df1,df2,on=['cust_id','cust_id'],how="outer",indicator=True)
      dfo=df[df['_merge']=='left_only']
      dfT =pd.merge(dfo,df2,on=['cust_id','cust_id'],how="right",indicator=True)
  </code></pre>
  
  <p>This is not working.
  Below is the error message:</p>
  
  <p><strong>ValueError: Cannot use name of an existing column for indicator column</strong></p>
  
  <p>I am not sure if there is any simpler or better approach to perform CDC.</p>
  
  <p><em>Sample data :</em></p>
  
  <p><strong>Master file :</strong> </p>
  
  <pre><code>   cust_id cust_name  cust_income cust_phone
  0      111     a            78000       sony
  1      222     b             8000        jio
  2      333     c           108000     iphone
  3      444     d           200000    iphoneX
  4      555     e            20000    samsung
  </code></pre>
  
  <p><strong>Delta file :</strong></p>
  
  <pre><code> cust_id cust_name  cust_income cust_phone
  0      222     b        20000          jio
  1      333     c        120000     iphoneX
  2      666     f        76000      oneplus
  </code></pre>
  
  <p><strong>Expected output:</strong></p>
  
  <pre><code>   cust_id cust_name  cust_income cust_phone
  0      111     a            78000       sony
  1      222     b            20000        jio
  2      333     c           120000     iphoneX
  3      444     d           200000    iphoneX
  4      555     e            20000    samsung
  5.     666     f           76000     oneplus
  </code></pre>