In [1]:

    

import pandas as pd


    

In [2]:

    

df = pd.DataFrame([[1, 3], [2, 4]], columns=['A', 'B'])
df


    

    
Out[2]:






  

    

      

      
A
      
B
    
  
  

    

      
0
      
1
      
3
    
    

      
1
      
2
      
4
    
  

In [3]:

    

df2 = pd.DataFrame([[1, 5], [1, 6]], columns=['A', 'C'])
df2


    

    
Out[3]:






  

    

      

      
A
      
C
    
  
  

    

      
0
      
1
      
5
    
    

      
1
      
1
      
6
    
  

In [4]:

    

df.merge(df2, how='left', on='A')  # merges on columns A


    

    
Out[4]:






  

    

      

      
A
      
B
      
C
    
  
  

    

      
0
      
1
      
3
      
5.0
    
    

      
1
      
1
      
3
      
6.0
    
    

      
2
      
2
      
4
      
NaN
    
  

In [5]:

    

df2.drop_duplicates(subset=['A'], inplace=True)


    

In [6]:

    

df.merge(df2, how='left', on='A')


    

    
Out[6]:






  

    

      

      
A
      
B
      
C
    
  
  

    

      
0
      
1
      
3
      
5.0
    
    

      
1
      
2
      
4
      
NaN
    
  

In [ ]: