accept indexes as wide-mode spec

Author: nicolaskruchten

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

@@ -1241,6 +1241,7 @@ def build_dataframe(args, constructor):
             args["wide_variable"] = args["y"] if wide_y else args["x"]
             if df_provided and args["wide_variable"] is df_input.columns:
                 var_name = df_input.columns.name
+            if isinstance(args["wide_variable"], pd.Index):
                 args["wide_variable"] = list(args["wide_variable"])
             if var_name in [None, "value", "index"] or (
                 df_provided and var_name in df_input

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

@@ -658,7 +658,7 @@ def append_special_case(df_in, args_in, args_expect, df_expect):
         dict(
             index=[7, 8, 7, 8],
             _value=[1, 2, 3, 4],
-            variable=["b", "b", "value", "value",],
+            variable=["b", "b", "value", "value"],
         )
     ),
 )
@@ -675,6 +675,16 @@ def append_special_case(df_in, args_in, args_expect, df_expect):
         dict(c=[7, 8, 7, 8], d=["a", "a", "b", "b"], value=[1, 2, 3, 4])
     ),
 )
+# y = columns
+df = pd.DataFrame(dict(a=[1, 2], b=[3, 4]), index=[7, 8])
+df.index.name = "c"
+df.columns.name = "d"
+append_special_case(
+    df_in=df,
+    args_in=dict(x=df.index, y=df.columns[:1], color=None),
+    args_expect=dict(x="c", y="value", color="variable"),
+    df_expect=pd.DataFrame(dict(c=[7, 8], variable=["a", "a"], value=[1, 2])),
+)
 
 
 @pytest.mark.parametrize("df_in, args_in, args_expect, df_expect", special_cases)