Bug Report: Template updatemenus and annotations not transferred to figures

Bug Report: Template updatemenus and annotations not transferred to figures

Description
When defining updatemenus and annotations in a Plotly template, they are not properly transferred to figures that use the template. While other template properties (like colors, fonts, etc.) are transferred correctly, updatemenus and annotations are created as empty lists.

Expected Behavior
All layout properties defined in a template, including updatemenus and annotations, should be transferred to figures that use the template.

Actual Behavior

• fig.layout.updatemenus and fig.layout.annotations are created (not None)
• However, they are empty lists, losing all content defined in the template
• Other template properties (like paper_bgcolor) are transferred correctly

Minimal Reproducible Example

import plotly.graph_objects as go
import plotly.io as pio
import numpy as np

# Create template with updatemenus and annotations
my_template = go.layout.Template(
    layout=dict(
        updatemenus=[
            dict(
                buttons=[
                    dict(
                        label="View 1",
                        method="relayout",
                        args=[{"scene.camera.eye": dict(x=1, y=1, z=1)}],
                    ),
                ],
                direction="down",
                showactive=True,
                x=0.1,
                y=1.1,
            ),
        ],
        annotations=[
            dict(
                text="Test annotation",
                x=0.5,
                y=1.1,
                xref="paper",
                yref="paper",
                showarrow=False,
            ),
        ],
        paper_bgcolor="rgb(240,240,240)",  # This works correctly
    )
)

# Register template
pio.templates["my_template"] = my_template

# Create figure with template
fig = go.Figure(
    data=[go.Scatter3d(
        x=np.random.normal(0, 1, 100),
        y=np.random.normal(0, 1, 100),
        z=np.random.normal(0, 1, 100),
        mode="markers",
    )]
)
fig.update_layout(template="my_template")

# Check results
print("Template updatemenus length:", len(my_template.layout.updatemenus))  # 1
print("Figure updatemenus length:", len(fig.layout.updatemenus))  # 0
print("Template annotations length:", len(my_template.layout.annotations))  # 1
print("Figure annotations length:", len(fig.layout.annotations))  # 0

Current Workaround
The only workaround is to manually apply the updatemenus and annotations after applying the template:

fig.update_layout(
    updatemenus=my_template.layout.updatemenus,
    annotations=my_template.layout.annotations,
)

Environment

• Python: 3.11.7
• Plotly: 5.24.1
• OS: Linux

Additional Context
This issue affects any template that tries to define interactive UI elements like buttons or annotations. The workaround requires additional code and makes templates less useful for defining reusable UI components.

Issue にある最小再現可能例から始め、fig.update_layout(template="my_template") がどのように layout プロパティを適用するかを追跡します。template と figure の updatemenus および annotations を比較し、それらの内容が転送される一方で paper_bgcolor が正しいままであることを示す回帰テストを追加します。