fix case with two slices, test added

Author: anzor

pandas/core/indexing.py

@@ -2376,7 +2376,10 @@ def ravel(i):
 
                 # single indexer
                 if len(indexer) > 1 and not multiindex_indexer:
-                    len_indexer = len(indexer[1])
+                    if isinstance(indexer[1], slice):
+                        len_indexer = len(obj.loc[indexer[1]].axes[1])
+                    else:
+                        len_indexer = len(indexer[1])
                     ser_values = (
                         np.tile(ser_values, len_indexer).reshape(len_indexer, -1).T
                     )

pandas/tests/indexing/test_loc.py

@@ -3330,3 +3330,10 @@ def test_loc_set_series_to_multiple_columns(self):
             [[10, 10, 10], [20, 20, 20], [30, 30, 30]], columns=list("ABC")
         )
         tm.assert_frame_equal(df, expected)
+
+        df = DataFrame([[1, 2, 3], [4, 5, 6], [7, 8, 9]], columns=list("ABC"))
+        df.loc[:, "A":"C"] = Series([10, 20, 30])
+        expected = DataFrame(
+            [[10, 10, 10], [20, 20, 20], [30, 30, 30]], columns=list("ABC")
+        )
+        tm.assert_frame_equal(df, expected)