How to do “(df1 & not df2)” dataframe merge in pandas?

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I just upgraded to version 0.17.0 RC1 which was released 10 days ago.
Just found out that pd.merge() have new argument in this new release called indicator=True to acheive this in pandonic way!!

df=pd.merge(df1,df2,on=['x','y'],how="outer",indicator=True)
df=df[df['_merge']=='left_only']

indicator: Add a column to the output DataFrame called _merge with information on the source of each row. _merge is Categorical-type and takes on a value of left_only for observations whose merge key only appears in ‘left’ DataFrame, right_only for observations whose merge key only appears in ‘right’ DataFrame, and both if the observation’s merge key is found in both.

http://pandas-docs.github.io/pandas-docs-travis/merging.html#database-style-dataframe-joining-merging

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