title: How to append one dataframe to another dataframe without duplicate
body: <p>I am trying to append one data frame with another data frame, but every 
  time I run the script it is keep appending the same row multiple times, but it 
  should not append the same dataframe in multiple times, need some suggestions 
  on this?                                                                     </p>
  
  <pre><code>    import pandas as pd
      from datetime import timedelta
      import glob
      directory1= r'path'
      files=glob.glob(directory1 + "\*.xls")
      for file in files:
         df= pd.read_excel(file,index_col=None, header=0)
      df1 = df[:-1]
      Average=df1['amount'].mean()
      Median=df1['amount'].median()
      val=20
      target=pd.read_excel('path\file.xlsx',sheet_name='Sheet1')
      date=target.iloc[1]
      df05= date['Week']+timedelta(days=7)
      sa=pd.Series([df05,Average,Median,val],index=['Week(Sunday)','Average 
      Amount','Median','Target'])
       target=target.append(sa,ignore_index=True,verify_integrity=True)
      writer=pd.ExcelWriter('path\file.xlsx',engine='xlsxwriter')
      target.to_excel(writer,sheet_name='Sheet1',index=False)
      writer.save()   
  </code></pre>