Fix: Don't modify global warnings.formatwarning

CHANGELOG.md

@@ -4,6 +4,9 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## Unreleased
 
+### Fixed
+- Fix issue where plotly was changing the global warnings format [[#5472](https://github.com/plotly/plotly.py/issues/5472)]
+
 ## [6.5.2] - 2026-01-14
 
 ### Fixed

plotly/matplotlylib/renderer.py

@@ -14,14 +14,6 @@
 from plotly.matplotlylib import mpltools
 
 
-# Warning format
-def warning_on_one_line(msg, category, filename, lineno, file=None, line=None):
-    return "%s:%s: %s:\n\n%s\n\n" % (filename, lineno, category.__name__, msg)
-
-
-warnings.formatwarning = warning_on_one_line
-
-
 class PlotlyRenderer(Renderer):
     """A renderer class inheriting from base for rendering mpl plots in plotly.
 

plotly/tools.py

@@ -55,14 +55,6 @@
 ALTERNATIVE_HISTNORM = "probability"
 
 
-# Warning format
-def warning_on_one_line(message, category, filename, lineno, file=None, line=None):
-    return "%s:%s: %s:\n\n%s\n\n" % (filename, lineno, category.__name__, message)
-
-
-warnings.formatwarning = warning_on_one_line
-
-
 ### mpl-related tools ###
 def mpl_to_plotly(fig, resize=False, strip_style=False, verbose=False):
     """Convert a matplotlib figure to plotly dictionary and send.

tests/test_core/test_warnings_format.py

@@ -0,0 +1,65 @@
+"""Test that plotly doesn't modify global warnings format (Issue #5472)"""
+import warnings
+import sys
+from unittest import TestCase
+
+
+class TestWarningsFormat(TestCase):
+    """Test that importing plotly modules doesn't change warnings.formatwarning"""
+
+    def test_import_plotly_does_not_change_warnings_format(self):
+        """Importing plotly should not modify the global warnings format"""
+        # Store the original format
+        original_format = warnings.formatwarning
+
+        # Import plotly modules that previously modified warnings.formatwarning
+        # We need to reimport to test the current code state
+        import importlib
+
+        # Force reimport of tools module to test current state
+        if 'plotly.tools' in sys.modules:
+            importlib.reload(sys.modules['plotly.tools'])
+        else:
+            import plotly.tools
+
+        # Check that warnings.formatwarning is still the original
+        self.assertIs(
+            warnings.formatwarning, 
+            original_format,
+            "Importing plotly.tools changed warnings.formatwarning globally"
+        )
+
+    def test_import_matplotlylib_renderer_does_not_change_warnings_format(self):
+        """Importing matplotlylib.renderer should not modify the global warnings format"""
+        # Store the original format
+        original_format = warnings.formatwarning
+
+        import importlib
+
+        # Force reimport of renderer module to test current state  
+        if 'plotly.matplotlylib.renderer' in sys.modules:
+            importlib.reload(sys.modules['plotly.matplotlylib.renderer'])
+        else:
+            import plotly.matplotlylib.renderer
+
+        # Check that warnings.formatwarning is still the original
+        self.assertIs(
+            warnings.formatwarning,
+            original_format,
+            "Importing plotly.matplotlylib.renderer changed warnings.formatwarning globally"
+        )
+
+    def test_warnings_format_unchanged_after_multiple_imports(self):
+        """Multiple imports should not change warnings format"""
+        original_format = warnings.formatwarning
+
+        # Import both modules
+        import plotly.tools
+        import plotly.matplotlylib.renderer
+
+        # Verify format is unchanged
+        self.assertIs(
+            warnings.formatwarning,
+            original_format,
+            "warnings.formatwarning was changed after importing plotly modules"
+        )