title: ValueError: Cannot use name of an existing column for indicator column
body: <p>I need to work on a problem where I will have a data frame,say df, with Name &amp; age &amp; I need to generate another dataframe with name &amp; gender in for loop &amp; I need to merge the data frame generated in for loop with df to get gender in df. So I tried below code before solving my problem</p>
  
  <pre><code>import pandas as pd
  d = {'Age': [45, 38], 'Name': ['John', 'Emily']}
  df = pd.DataFrame(data=d)
  d1={'Gender':['M'],'Name':['John']}
  df1=pd.DataFrame(data=d1)
  
  df3 = df.merge(df1, on=['Name'], how='left', indicator=True)
  df3
  
  d2={'Gender':['F'],'Name':['Emily']}
  df4=pd.DataFrame(data=d2)
  df5=df3.merge(df4, on=['Name'], how='left', indicator=True)
  </code></pre>
  
  <p>I'm getting following error while I'm running the last line.</p>
  
  <pre><code> "Cannot use name of an existing column for indicator column")
  
  ValueError: Cannot use name of an existing column for indicator column
  </code></pre>
  
  <p>Can you please suggest me how to solve this problem in python 3.x?</p>