gh-144975: Fix wave.Wave_write.setframerate() validation order

Validate the frame rate after rounding to an integer, not before. This prevents values like 0.5 from passing validation (0.5 > 0) but then rounding to 0, which would cause a confusing delayed error "sampling rate not specified" when writing frames. With this fix, setframerate(0.5) immediately raises "bad frame rate", providing clear feedback at the point of the error.
python · mbeijen · Feb 18, 2026 · Feb 18, 2026 · Feb 18, 2026 · 027364153a751a8d3b907ccbea627a9be896c902
commit 027364153a751a8d3b907ccbea627a9be896c902
diff --git a/Lib/test/test_wave.py b/Lib/test/test_wave.py
@@ -207,6 +207,39 @@ def test_open_in_write_raises(self):
             support.gc_collect()
             self.assertIsNone(cm.unraisable)
 
+    def test_setframerate_rounds_then_validates(self):
+        """Test that setframerate rounds before validation"""
+        # Test that framerates that round to 0 or negative are rejected
+        with wave.open(io.BytesIO(), 'wb') as f:
+            f.setnchannels(1)
+            f.setsampwidth(2)
+            # 0.5 rounds to 0, should raise
+            with self.assertRaises(wave.Error):
+                f.setframerate(0.5)
+            # 0.4 rounds to 0, should raise
+            with self.assertRaises(wave.Error):
+                f.setframerate(0.4)
+            # Negative values should still raise
+            with self.assertRaises(wave.Error):
+                f.setframerate(-1)
+            with self.assertRaises(wave.Error):
+                f.setframerate(-0.5)
+            # 0 should raise
+            with self.assertRaises(wave.Error):
+                f.setframerate(0)
+
+            # Valid values that round to positive integers should work
+            f.setframerate(1.4)  # rounds to 1
+            self.assertEqual(f.getframerate(), 1)
+            f.setframerate(1.5)  # rounds to 2
+            self.assertEqual(f.getframerate(), 2)
+            f.setframerate(1.6)  # rounds to 2
+            self.assertEqual(f.getframerate(), 2)
+            f.setframerate(44100.4)  # rounds to 44100
+            self.assertEqual(f.getframerate(), 44100)
+            f.setframerate(44100.5)  # rounds to 44100
+            self.assertEqual(f.getframerate(), 44100)
+
 
 class WaveOpen(unittest.TestCase):
     def test_open_pathlike(self):

diff --git a/Lib/wave.py b/Lib/wave.py
@@ -493,9 +493,10 @@ def getsampwidth(self):
     def setframerate(self, framerate):
         if self._datawritten:
             raise Error('cannot change parameters after starting to write')
+        framerate = int(round(framerate))
         if framerate <= 0:
             raise Error('bad frame rate')
-        self._framerate = int(round(framerate))
+        self._framerate = framerate
 
     def getframerate(self):
         if not self._framerate:

diff --git a/Misc/NEWS.d/next/Library/2026-02-18-21-45-00.gh-issue-144975.Ab3XyZ.rst b/Misc/NEWS.d/next/Library/2026-02-18-21-45-00.gh-issue-144975.Ab3XyZ.rst
@@ -0,0 +1,3 @@
+:meth:`wave.Wave_write.setframerate` now validates the frame rate after
+rounding to an integer, preventing values like ``0.5`` from being accepted
+and causing confusing errors later. Patch by Michiel Beijen.