fix pandas-dev#18030

Author: Randolf Scholz

pandas/core/reshape/pivot.py

@@ -203,18 +203,32 @@ def __internal_pivot_table(
                 to_unstack.append(name)
         table = agged.unstack(to_unstack)
 
-    if not dropna:
-        if isinstance(table.index, MultiIndex):
-            m = MultiIndex.from_arrays(
-                cartesian_product(table.index.levels), names=table.index.names
-            )
-            table = table.reindex(m, axis=0)
-
-        if isinstance(table.columns, MultiIndex):
-            m = MultiIndex.from_arrays(
-                cartesian_product(table.columns.levels), names=table.columns.names
-            )
-            table = table.reindex(m, axis=1)
+    # BEGIN Issue #18030
+    # Commenting these lines in view of #18030.
+    # The cartesian product makes little sense and deprecation of this behaviour should be considered.
+    # It is unexpected that a pivot operation returns a larger index than is given.
+    # Secondly, this behaviour was never documented. The documentation says
+    #
+    # dropna:bool, default True
+    #
+    #   Do not include columns whose entries are all NaN.
+    #
+    # However the code below creates rows.
+
+    # if not dropna:
+    #     if isinstance(table.index, MultiIndex):
+    #         m = MultiIndex.from_arrays(
+    #             cartesian_product(table.index.levels), names=table.index.names
+    #         )
+    #         table = table.reindex(m, axis=0)
+    #
+    #     if isinstance(table.columns, MultiIndex):
+    #         m = MultiIndex.from_arrays(
+    #             cartesian_product(table.columns.levels), names=table.columns.names
+    #         )
+    #         table = table.reindex(m, axis=1)
+
+    # END Issue #18030
 
     if isinstance(table, ABCDataFrame):
         table = table.sort_index(axis=1)