implement pull request plotly#3731 and add tests to fix plotly#3065

Author: amiteitan

plotly/shapeannotation.py

@@ -4,6 +4,9 @@
 def _mean(x):
     if len(x) == 0:
         raise ValueError("x must have positive length")
+
+    if len(x) == 2 and x[0] == x[1]:
+        return x[0]
     return float(sum(x)) / len(x)
 
 

tests/test_optional/test_autoshapes/test_annotated_shapes.py

@@ -51,6 +51,25 @@ def multi_plot_fixture():
         fig.add_trace(go.Scatter(x=[], y=[]), row=r, col=c)
     return fig
 
+from datetime import datetime, timedelta
+def test_add_shape_with_dates():
+    start_date = datetime(2025, 1, 1)
+    end_date = datetime(2025, 10, 10)
+    dates = []
+    current_date = start_date
+    while current_date <= end_date:
+        dates.append(current_date.strftime("%Y-%m-%d"))
+        current_date += timedelta(weeks=4)
+    print(dates)
+    fig = go.Figure(
+        data=[go.Scatter(x=[x for x in range(1, 20, 2)], y=dates)],
+        layout=go.Layout(
+            title=go.layout.Title(text="A Figure Specified By A Graph Object")
+        )
+    )
+    fig.add_vline(x="2025-06-24", annotation_text="test")
+    assert len(fig.layout.annotations) == 1
+
 
 # Make sure adding a shape without specifying an annotation doesn't add any annotations
 def test_add_shape_no_annotation(multi_plot_fixture):