 = pd.DataFrame(     {'month': ['jan', 'feb', 'mar', 'apr', 'may', 'jun', 'jul', 'aug', 'sep',                'oct', 'nov', 'dec'],      '0000_val': [0, 0, 0, 0, 0, 0, 0, 0, 0, 00, 0, 0]})  right_0000 = pd.DataFrame({'month': ['jan', 'feb'], '0000_val': [0, 0]})  right_0000_target = pd.DataFrame(     {'month': ['jan', 'feb', 'mar', 'apr', 'may', 'jun', 'jul', 'aug', 'sep',                'oct', 'nov', 'dec'],      '0000_target_val': [0, 0, 0, 0, 0, 0, 0, 0, 00, 00, 00, 00]})  df_00_00 = pd.merge(left_0000, right_0000, how='outer') df_00_00_target = pd.merge(df_00_00, right_0000_target, how='outer') 