From c8324eea84c762842c29fe8193e87ac89129e96b Mon Sep 17 00:00:00 2001
From: Tim Hoffmann <2836374+timhoffm@users.noreply.github.com>
Date: Fri, 30 Oct 2020 03:18:28 +0100
Subject: [PATCH] Backport PR #18839: MNT: make sure we do not mutate input in
 Text.update

---
 lib/matplotlib/tests/test_text.py | 12 ++++++++++++
 lib/matplotlib/text.py            |  2 ++
 2 files changed, 14 insertions(+)

diff --git a/lib/matplotlib/tests/test_text.py b/lib/matplotlib/tests/test_text.py
index 70855e6d879f..8d91b1318d88 100644
--- a/lib/matplotlib/tests/test_text.py
+++ b/lib/matplotlib/tests/test_text.py
@@ -8,9 +8,11 @@
 
 import matplotlib as mpl
 from matplotlib.backend_bases import MouseEvent
+from matplotlib.font_manager import FontProperties
 import matplotlib.patches as mpatches
 import matplotlib.pyplot as plt
 from matplotlib.testing.decorators import check_figures_equal, image_comparison
+from matplotlib.text import Text
 
 
 needs_usetex = pytest.mark.skipif(
@@ -689,3 +691,13 @@ def test_fontproperties_kwarg_precedence():
     text2 = plt.ylabel("counts", size=40.0, fontproperties='Times New Roman')
     assert text1.get_size() == 40.0
     assert text2.get_size() == 40.0
+
+
+def test_update_mutate_input():
+    inp = dict(fontproperties=FontProperties(weight="bold"),
+               bbox=None)
+    cache = dict(inp)
+    t = Text()
+    t.update(inp)
+    assert inp['fontproperties'] == cache['fontproperties']
+    assert inp['bbox'] == cache['bbox']
diff --git a/lib/matplotlib/text.py b/lib/matplotlib/text.py
index 3b30a4cfb502..efe4450f4fba 100644
--- a/lib/matplotlib/text.py
+++ b/lib/matplotlib/text.py
@@ -167,6 +167,8 @@ def __init__(self,
 
     def update(self, kwargs):
         # docstring inherited
+        # make a copy so we do not mutate user input!
+        kwargs = dict(kwargs)
         sentinel = object()  # bbox can be None, so use another sentinel.
         # Update fontproperties first, as it has lowest priority.
         fontproperties = kwargs.pop("fontproperties", sentinel)