Improve astuple performance for nested atomic sequences

bench/test_benchmarks.py

@@ -177,6 +177,22 @@ def test_astuple_atomic():
         at(c)
 
 
+@attrs.define
+class NestedAtomicFields:
+    sequence: list[int] = attrs.Factory(lambda: list(range(100)))
+
+
+def test_astuple_nested_atomic():
+    """
+    Benchmark atomic values nested in a sequence.
+    """
+    c = NestedAtomicFields()
+    at = attrs.astuple
+
+    for _ in range(ROUNDS):
+        at(c)
+
+
 class TestCachedProperties:
     @attrs.define
     class Slotted:

changelog.d/1636.change.md

@@ -0,0 +1 @@
+Improved `attrs.astuple()` performance for atomic values nested in sequences by avoiding unnecessary attrs-class detection.

src/attr/_funcs.py

@@ -301,7 +301,7 @@ def astuple(
                             tuple_factory=tuple_factory,
                             retain_collection_types=retain,
                         )
-                        if has(j.__class__)
+                        if type(j) not in _ATOMIC_TYPES and has(j.__class__)
                         else j
                     )
                     for j in v