merge

Lib/test/test_heapq.py

@@ -158,6 +158,15 @@ class TestHeap:
         self.assertEqual(sorted(chain(*inputs)), list(self.module.merge(*inputs)))
         self.assertEqual(list(self.module.merge()), [])
 
+    def test_merge_does_not_suppress_index_error(self):
+        # Issue 19018: Heapq.merge suppresses IndexError from user generator
+        def iterable():
+            s = list(range(10))
+            for i in range(20):
+                yield s[i]       # IndexError when i > 10
+        with self.assertRaises(IndexError):
+            list(self.module.merge(iterable(), iterable()))
+
     def test_merge_stability(self):
         class Int(int):
             pass

Misc/ACKS

@@ -394,6 +394,7 @@ Nils Fischbeck
 Frederik Fix
 Matt Fleming
 Hernán Martínez Foffani
+Artem Fokin
 Arnaud Fontaine
 Michael Foord
 Amaury Forgeot d'Arc

Misc/NEWS

@@ -18,6 +18,9 @@ Library
 - Issue #17324: Fix http.server's request handling case on trailing '/'. Patch
   contributed by Vajrasky Kok.
 
+- Issue #19018: The heapq.merge() function no longer suppresses IndexError
+  in the underlying iterables.
+
 - Issue #18784: The uuid module no more attempts to load libc via ctypes.CDLL,
   if all necessary functions are already found in libuuid.
   Patch by Evgeny Sologubov.