is it better to do union of dataframes code example

Example 1: union df pandas

pd.concat([df1, df2])

Example 2: take union of two dataframes pandas

m = {'left_only': 'df1', 'right_only': 'df2', 'both': 'df1, df2'}

result = df1.merge(df2, on=['A'], how='outer', indicator='B')
result['B'] = result['B'].map(m)

result