more comments

Author: debnathshoham

pandas/core/frame.py

@@ -275,8 +275,8 @@
 ----------%s
 right : DataFrame or named Series
     Object to merge with.
-how : {'left', 'right', 'outer', 'inner', 'cross',
- 'anti_left', 'anti_right', 'anti_full'}, default 'inner'
+how : {'left', 'right', 'outer', 'inner', 'cross', 'anti_left', \
+'anti_right', 'anti_full'}, default 'inner'
     Type of merge to be performed.
 
     * left: use only keys from left frame, similar to a SQL left outer join;
@@ -473,14 +473,18 @@
 1  2  8
 2  4  9
 >>> df1.merge(df2, on="C", how="anti_left")
+# because `7` is common in column `C` it's dropped from df1
    A  C   B
 0  1  5 NaN
 1  2  6 NaN
 >>> df1.merge(df2, on="C", how="anti_right")
+# because `7` is common in column `C` it's dropped from df2
     A  C  B
 0 NaN  8  2
 1 NaN  9  4
 >>> df1.merge(df2, on="C", how="anti_full")
+# because `7` is common in column `C` it's dropped from both
+# df1 and df2, then outer merged
      A  C    B
 0  1.0  5  NaN
 1  2.0  6  NaN

pandas/tests/reshape/merge/test_merge_anti.py

@@ -24,6 +24,7 @@ class Test_AntiJoin:
         ],
     )
     def test_basic_anti_index(self, how, exp_index, exp_values):
+        # basic test containing NaNs w/o on param
         left = DataFrame({"A": [1, 2, 3], "C": [10, 20, 30]}, index=["a", "b", "c"])
         right = DataFrame({"B": [1, 2, 4], "C": [10, 20, 40]}, index=["a", "b", "d"])
         expected = DataFrame(
@@ -68,6 +69,7 @@ def test_basic_anti_index(self, how, exp_index, exp_values):
         ],
     )
     def test_basic_anti_on(self, on, how, data):
+        # basic test containing NaNs with on param
         left = DataFrame({"A": [1, 2, 3], "C": [5, 6, 7]}, index=["a", "b", "c"])
         right = DataFrame({"B": [1, 2, 4], "C": [7, 8, 9]}, index=["a", "b", "d"])
         expected = DataFrame(data, columns=["A", "C", "B"])
@@ -105,6 +107,7 @@ def test_basic_anti_on(self, on, how, data):
         ],
     )
     def test_basic_anti_lefton_righton(self, expected, how, left_on, right_on):
+        # basic test containing NaNs with left_on / right_on params
         left = DataFrame({"A": [1, 2, 3], "C": [5, 6, 7]}, index=["a", "b", "c"])
         right = DataFrame({"B": [1, 2, 4], "C": [7, 8, 9]}, index=["a", "b", "d"])
         result = merge(
@@ -164,6 +167,7 @@ def test_basic_anti_lefton_righton(self, expected, how, left_on, right_on):
         ],
     )
     def test_anti_index_with_col(self, expected, how):
+        # basic test containing NaNs with left_index and right_on params
         left = DataFrame(
             {"A": [1, 2, 3], "B": [4, 5, 6], "C": [5, 6, 7]}, index=["a", "b", "c"]
         )
@@ -229,6 +233,7 @@ def test_anti_index_with_col(self, expected, how):
         ],
     )
     def test_anti_multicol(self, expected, how, on):
+        # test with multicol with and w/o on param
         right = DataFrame({"B": [5, 5, 9], "C": [4, 6, 7], "D": ["a", "b", "d"]})
         left = DataFrame(
             {"A": [1, 2, 3], "B": [4, 5, 6], "C": [5, 6, 7]}, index=["a", "b", "c"]