Avoid unhelpful full diff for unequal range comparisons

changelog/6772.improvement.rst

@@ -0,0 +1 @@
+Improved assertion failure output for unequal ``range`` objects by avoiding unhelpful full diffs while retaining sequence difference details.

src/_pytest/assertion/_compare_any.py

@@ -79,6 +79,9 @@ def _compare_eq_any(
             )
 
         if isiterable(left) and isiterable(right):
+            if isinstance(left, range) and isinstance(right, range):
+                # Sequence output already covers ranges; skip the noisy repr diff.
+                return
             yield from _compare_eq_iterable(
                 left, right, highlighter, verbose, truncation_budget
             )

src/_pytest/assertion/_compare_sequence.py

@@ -52,7 +52,11 @@ def _compare_eq_sequence(
     comparing_bytes = isinstance(left, bytes) and isinstance(right, bytes)
     len_left = len(left)
     len_right = len(right)
-    for i in range(min(len_left, len_right)):
+    common_length = min(len_left, len_right)
+    if isinstance(left, range) and isinstance(right, range):
+        # First two items fix start and step, so the prefix check is O(1).
+        common_length = min(common_length, 2)
+    for i in range(common_length):
         if left[i] != right[i]:
             if comparing_bytes:
                 # when comparing bytes, we want to see their ascii representation

testing/test_assertion.py

@@ -796,6 +796,49 @@ def test_list_different_lengths(self) -> None:
         assert expl is not None
         assert len(expl) > 1
 
+    def test_range_different_lengths(self) -> None:
+        assert callequal(range(5), range(7)) == [
+            "range(0, 5) == range(0, 7)",
+            "",
+            "Right contains 2 more items, first extra item: 5",
+        ]
+        assert callequal(range(7), range(5)) == [
+            "range(0, 7) == range(0, 5)",
+            "",
+            "Left contains 2 more items, first extra item: 5",
+        ]
+        # Verbose adds no full diff for ranges.
+        assert callequal(range(5), range(7), verbose=1) == callequal(range(5), range(7))
+
+    def test_range_different_items(self) -> None:
+        assert callequal(range(5), range(1, 6)) == [
+            "range(0, 5) == range(1, 6)",
+            "",
+            "At index 0 diff: 0 != 1",
+        ]
+        assert callequal(range(0, 10, 2), range(0, 13, 3)) == [
+            "range(0, 10, 2) == range(0, 13, 3)",
+            "",
+            "At index 1 diff: 2 != 3",
+        ]
+        assert callequal(range(5), range(1, 6), verbose=1) == callequal(
+            range(5), range(1, 6)
+        )
+
+    def test_range_huge_comparison_is_fast(self, pytester: Pytester) -> None:
+        pytester.makepyfile(
+            """
+            def test_huge_range():
+                assert range(10**12) == range(10**12 + 2)
+            """
+        )
+        result = pytester.runpytest_subprocess("-v", timeout=10)
+        assert result.ret == 1
+        result.stdout.fnmatch_lines(
+            ["E*Right contains 2 more items, first extra item: 1000000000000*"]
+        )
+        result.stdout.no_fnmatch_line("E*Full diff*")
+
     def test_list_wrap_for_multiple_lines(self) -> None:
         long_d = "d" * 80
         l1 = ["a", "b", "c"]