worked on review comments

Author: iynehz

pandas/core/frame.py

@@ -7927,6 +7927,10 @@ def explode(
             For multiple columns, specify a non-empty list with each element
             be str or tuple, and all specified columns their list-like data
             on same row of the frame must have matching length.
+
+            .. versionadded:: 1.3.0
+                Multi-column explode
+
         ignore_index : bool, default False
             If True, the resulting index will be labeled 0, 1, …, n - 1.
 
@@ -7973,6 +7977,8 @@ def explode(
         2         []  1         []
         3     [3, 4]  1     [d, e]
 
+        Single-column explode.
+
         >>> df.explode('A')
              A  B          C
         0    0  1  [a, b, c]
@@ -7983,6 +7989,8 @@ def explode(
         3    3  1     [d, e]
         3    4  1     [d, e]
 
+        Multi-column explode.
+
         >>> df.explode(list('AC'))
              A  B    C
         0    0  1    a
@@ -8005,7 +8013,7 @@ def explode(
         elif isinstance(column, list) and all(
             map(lambda c: is_scalar(c) or isinstance(c, tuple), column)
         ):
-            if len(column) == 0:
+            if not column:
                 raise ValueError("column must be nonempty")
             if len(column) > len(set(column)):
                 raise ValueError("column must be unique")

pandas/tests/frame/methods/test_explode.py

@@ -21,17 +21,20 @@ def test_error():
     with pytest.raises(ValueError, match="columns must be unique"):
         df.explode("A")
 
+
+def test_error_multi_columns():
     # GH 39240
+    df = pd.DataFrame(
+        {"A": pd.Series([[0, 1, 2], np.nan, [], (3, 4)], index=list("abcd")), "B": 1}
+    )
     df1 = df.assign(C=[["a", "b", "c"], "foo", [], ["d", "e", "f"]])
     df1.columns = list("ABC")
     with pytest.raises(ValueError, match="columns must have matching element counts"):
         df1.explode(list("AC"))
 
-    # GH 39240
     with pytest.raises(ValueError, match="column must be nonempty"):
         df1.explode([])
 
-    # GH 39240
     df2 = df.assign(C=[["a", "b", "c"], "foo", [], "d"])
     df2.columns = list("ABC")
     with pytest.raises(ValueError, match="columns must have matching element counts"):
@@ -207,19 +210,23 @@ def test_multi_columns():
     # GH 39240
     df = pd.DataFrame(
         {
-            "A": pd.Series([[0, 1, 2], np.nan, [], (3, 4)], index=list("abcd")),
+            "A": pd.Series(
+                [[0, 1, 2], np.nan, [], (3, 4), np.nan], index=list("abcde")
+            ),
             "B": 1,
-            "C": [["a", "b", "c"], "foo", [], ["d", "e"]],
+            "C": [["a", "b", "c"], "foo", [], ["d", "e"], np.nan],
         }
     )
     result = df.explode(list("AC"))
     expected = pd.DataFrame(
         {
             "A": pd.Series(
-                [0, 1, 2, np.nan, np.nan, 3, 4], index=list("aaabcdd"), dtype=object
+                [0, 1, 2, np.nan, np.nan, 3, 4, np.nan],
+                index=list("aaabcdde"),
+                dtype=object,
             ),
             "B": 1,
-            "C": ["a", "b", "c", "foo", np.nan, "d", "e"],
+            "C": ["a", "b", "c", "foo", np.nan, "d", "e", np.nan],
         }
     )
     tm.assert_frame_equal(result, expected)