Don't modify the annotation passed to add_vline and friends

axis_spanning_shape_annotation filled in the annotation it was given
(text from annotation_* kwargs, and x/y/xanchor/yanchor from the shape)
in place. When the same dict or go.layout.Annotation was passed to
several add_vline/add_hline/add_vrect/add_hrect calls, the first call
left x/y in it, and later calls only set positions that weren't set
already, so every annotation ended up at the first shape.

Work on a copy of the annotation instead.

Closes #3547

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

Author: adarshsm

CHANGELOG.md

@@ -17,6 +17,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 - Fix Plotly Express mutating lists passed to the `x` or `y` arguments in wide mode [[#5727](https://github.com/plotly/plotly.py/pull/5727)], with thanks to @cpruijsen for the contribution!
 - Fix `px.sunburst`, `px.treemap` and `px.icicle` listing sectors in a different order on every run when `path` is used with a Polars DataFrame; sectors now follow their order of first appearance for all dataframe backends [[#5766](https://github.com/plotly/plotly.py/pull/5766)], with thanks to @Irahan2 for the contribution!
 - Fix `mpl_to_plotly` conversion of matplotlib contour lines and line collections: close contour rings ending with `Z` codes, support dash styles, convert date x-axes, separate disjoint subpaths with `None` separators, hide line collection traces from the legend by default, and group consecutive same-style lines into single traces [[#5770](https://github.com/plotly/plotly.py/pull/5770)], with thanks to @robertoffmoura for the contribution!
+- Fix `add_vline`, `add_hline`, `add_vrect` and `add_hrect` modifying the dict or `go.layout.Annotation` passed as `annotation`, which placed every later shape's annotation at the first shape's position when the same `annotation` was reused [[#3547](https://github.com/plotly/plotly.py/issues/3547)], with thanks to @adarshsm for the contribution!
 
 ## [7.1.0] - 2026-09-15
 

plotly/shapeannotation.py

@@ -1,5 +1,6 @@
 # some functions defined here to avoid numpy import
 
+import copy
 import datetime
 
 
@@ -244,6 +245,10 @@ def axis_spanning_shape_annotation(annotation, shape_type, shape_args, kwargs):
     # go.layout.Annotation ?
     if annotation is None:
         annotation = dict()
+    else:
+        # Fill in a copy, so that an annotation passed in can be reused for
+        # other shapes without keeping this shape's text and position.
+        annotation = copy.copy(annotation)
     for k in annotation_keys:
         if k == "annotation_position":
             # don't set so that Annotation constructor doesn't complain

tests/test_optional/test_autoshapes/test_annotated_shapes.py

@@ -24,6 +24,7 @@
 import plotly.graph_objects as go
 from plotly.subplots import make_subplots
 from itertools import product
+import copy
 import os
 import pytest
 import json
@@ -282,6 +283,30 @@ def test_specify_annotation_as_dict(multi_plot_fixture):
     assert ret
 
 
+# Test that the annotation passed in isn't modified, so it can be reused for
+# several shapes
+@pytest.mark.parametrize(
+    "annotation",
+    [dict(font_color="red"), go.layout.Annotation(font_color="red")],
+    ids=["dict", "Annotation"],
+)
+def test_reuse_annotation(single_plot_fixture, annotation):
+    before = copy.deepcopy(annotation)
+    single_plot_fixture.add_vline(x=2, annotation_text="A", annotation=annotation)
+    single_plot_fixture.add_vline(x=3, annotation_text="B", annotation=annotation)
+    assert annotation == before
+    ret = len(single_plot_fixture.layout.annotations) == 2
+    for sh, d in zip(
+        single_plot_fixture.layout.annotations,
+        [
+            {"text": "A", "x": 2, "font.color": "red"},
+            {"text": "B", "x": 3, "font.color": "red"},
+        ],
+    ):
+        ret &= _cmp_partial_dict(sh, d)
+    assert ret
+
+
 # Test the default and coerced positions work
 def test_default_annotation_positions(multi_plot_fixture):
     # default position is (inside) top right