Fix unformatted placeholders in two ValueError messages

The error raised when adding a trace with `secondary_y=True` to a subplot
that was not created with the `secondary_y` spec, and the error raised for
an invalid `output_type` in `plotly.io.from_json`/`read_json`, were plain
strings that were never formatted, so users saw the literal
"{subplot_type}", "({row}, {col})" and "{output_type}". Format them like
the neighbouring messages in the same functions already do.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: David-Wu1119

plotly/_subplots.py

@@ -1425,7 +1425,7 @@ def _set_trace_grid_reference(trace, layout, grid_ref, row, col, secondary_y=Fal
 Subplot with type '{subplot_type}' at grid position ({row}, {col}) was not
 created with the secondary_y spec property set to True. See the docstring
 for the specs argument to plotly.subplots.make_subplots for more information.
-"""
+""".format(subplot_type=subplot_refs[0].subplot_type, row=row, col=col)
             )
         trace_kwargs = subplot_refs[1].trace_kwargs
     else:

plotly/io/_utils.py

@@ -38,7 +38,7 @@ def validate_coerce_output_type(output_type):
         raise ValueError(
             """
 Invalid output type: {output_type}
-    Must be one of: 'Figure', 'FigureWidget'"""
+    Must be one of: 'Figure', 'FigureWidget'""".format(output_type=output_type)
         )
     return cls
 

tests/test_core/test_subplots/test_make_subplots.py

@@ -2038,3 +2038,12 @@ def test_make_subplots_spacing_error():
         ValueError, match=r"^Vertical spacing must be between 0 and 1\.$"
     ):
         subplots.make_subplots(1, 1, vertical_spacing=1.01)
+
+
+def test_secondary_y_without_spec_error():
+    fig = subplots.make_subplots(rows=1, cols=2)
+    with pytest.raises(
+        ValueError,
+        match=r"Subplot with type 'xy' at grid position \(1, 2\) was not",
+    ):
+        fig.add_scatter(x=[1], y=[1], row=1, col=2, secondary_y=True)

tests/test_io/test_to_from_json.py

@@ -118,6 +118,11 @@ def test_from_json_invalid(fig1):
         pio.from_json(bad_json)
 
 
+def test_from_json_invalid_output_type(fig1):
+    with pytest.raises(ValueError, match="Invalid output type: Bogus"):
+        pio.from_json(pio.to_json(fig1), output_type="Bogus")
+
+
 def test_from_json_skip_invalid(fig1):
     dict1 = fig1.to_dict()