In pandas, you can use the following command:
pd.merge(df1,df2,on='key',how='left')
The following is the output to the preceding commands:
Output of the left join between the two tables
As expected of a left join, it retrieves all the unique values of the key present in the left-hand table (df1, in this case), as well as the corresponding values in the right-hand table. For the key values in the left-hand table for which it doesn't find a match in the right-hand table, it returns NaN.
Suppose we want to implement a right join between the two. This can be done in the two tools as shown here: