raise errors on multi-index in column/index in wide mode

Author: nicolaskruchten

packages/python/plotly/plotly/express/_core.py

@@ -1215,6 +1215,12 @@ def build_dataframe(args, constructor):
             )
         if df_provided and no_x and no_y:
             wide_mode = True
+            if isinstance(df_input.columns, pd.MultiIndex):
+                raise TypeError(
+                    "Data frame columns is a pandas MultiIndex. "
+                    "pandas MultiIndex is not supported by plotly express "
+                    "at the moment."
+                )
             args["wide_variable"] = list(df_input.columns)
             var_name = df_input.columns.name or "variable"
             if constructor == go.Funnel:
@@ -1251,6 +1257,12 @@ def build_dataframe(args, constructor):
             if no_x != no_y and args["orientation"] is None:
                 args["orientation"] = "v" if no_x else "h"
             if df_provided:
+                if isinstance(df_input.index, pd.MultiIndex):
+                    raise TypeError(
+                        "Data frame index is a pandas MultiIndex. "
+                        "pandas MultiIndex is not supported by plotly express "
+                        "at the moment."
+                    )
                 args["wide_cross"] = df_input.index
                 wide_cross_name = df_input.index.name or "index"
             else:

packages/python/plotly/plotly/tests/test_core/test_px/test_px_wide.py

@@ -628,3 +628,21 @@ def test_wide_mode_internal_special_cases(df_in, args_in, args_expect, df_expect
         df_out.sort_index(axis=1), df_expect.sort_index(axis=1),
     )
     assert args_out == args_expect
+
+
+def test_multi_index():
+    df = pd.DataFrame([[1, 2, 3, 4], [3, 4, 5, 6], [1, 2, 3, 4], [3, 4, 5, 6]])
+    df.index = [["a", "a", "b", "b"], ["c", "d", "c", "d"]]
+    with pytest.raises(TypeError) as err_msg:
+        px.scatter(df)
+        assert "pandas MultiIndex is not supported by plotly express" in str(
+            err_msg.value
+        )
+
+    df = pd.DataFrame([[1, 2, 3, 4], [3, 4, 5, 6], [1, 2, 3, 4], [3, 4, 5, 6]])
+    df.columns = [["e", "e", "f", "f"], ["g", "h", "g", "h"]]
+    with pytest.raises(TypeError) as err_msg:
+        px.scatter(df)
+        assert "pandas MultiIndex is not supported by plotly express" in str(
+            err_msg.value
+        )