Add B911: itertools.batched without strict= (#502)

Author: tjkuson

README.rst

@@ -258,6 +258,10 @@ This is meant to be enabled by developers writing visitors using the ``ast`` mod
 
 **B910**: Use Counter() instead of defaultdict(int) to avoid excessive memory use as the default dict will record missing keys with the default value when accessed.
 
+**B911**: ``itertools.batched()`` without an explicit `strict=` parameter set. ``strict=True`` causes the resulting iterator to raise a ``ValueError`` if the final batch is shorter than ``n``.
+
+The ``strict=`` argument was added in Python 3.13, so don't enable this flag for code that should work on <3.13.
+
 **B950**: Line too long. This is a pragmatic equivalent of
 ``pycodestyle``'s ``E501``: it considers "max-line-length" but only triggers
 when the value has been exceeded by **more than 10%**. ``noqa`` and ``type: ignore`` comments are ignored. You will no

bugbear.py

@@ -515,6 +515,7 @@ def visit_Call(self, node) -> None:
         self.check_for_b039(node)
         self.check_for_b905(node)
         self.check_for_b910(node)
+        self.check_for_b911(node)
 
         # no need for copying, if used in nested calls it will be set to None
         current_b040_caught_exception = self.b040_caught_exception
@@ -1757,6 +1758,18 @@ def check_for_b910(self, node: ast.Call) -> None:
         ):
             self.errors.append(B910(node.lineno, node.col_offset))
 
+    def check_for_b911(self, node: ast.Call) -> None:
+        if (
+            (isinstance(node.func, ast.Name) and node.func.id == "batched")
+            or (
+                isinstance(node.func, ast.Attribute)
+                and node.func.attr == "batched"
+                and isinstance(node.func.value, ast.Name)
+                and node.func.value.id == "itertools"
+            )
+        ) and not any(kw.arg == "strict" for kw in node.keywords):
+            self.errors.append(B911(node.lineno, node.col_offset))
+
 
 def compose_call_path(node):
     if isinstance(node, ast.Attribute):
@@ -2436,6 +2449,9 @@ def visit_Lambda(self, node) -> None:
 B910 = Error(
     message="B910 Use Counter() instead of defaultdict(int) to avoid excessive memory use"
 )
+B911 = Error(
+    message="B911 `itertools.batched()` without an explicit `strict=` parameter."
+)
 B950 = Error(message="B950 line too long ({} > {} characters)")
 
 
@@ -2449,5 +2465,6 @@ def visit_Lambda(self, node) -> None:
     "B908",
     "B909",
     "B910",
+    "B911",
     "B950",
 ]

tests/b911_py313.py

@@ -0,0 +1,24 @@
+import itertools
+from itertools import batched
+
+# Expect B911
+batched(range(3), 2)
+batched(range(3), n=2)
+batched(iterable=range(3), n=2)
+itertools.batched(range(3), 2)
+itertools.batched(range(3), n=2)
+itertools.batched(iterable=range(3), n=2)
+
+# OK
+batched(range(3), 2, strict=True)
+batched(range(3), n=2, strict=True)
+batched(iterable=range(3), n=2, strict=True)
+batched(range(3), 2, strict=False)
+batched(range(3), n=2, strict=False)
+batched(iterable=range(3), n=2, strict=False)
+itertools.batched(range(3), 2, strict=True)
+itertools.batched(range(3), n=2, strict=True)
+itertools.batched(iterable=range(3), n=2, strict=True)
+itertools.batched(range(3), 2, strict=False)
+itertools.batched(range(3), n=2, strict=False)
+itertools.batched(iterable=range(3), n=2, strict=False)

tests/test_bugbear.py

@@ -59,6 +59,7 @@
     B908,
     B909,
     B910,
+    B911,
     B950,
     BugBearChecker,
     BugBearVisitor,
@@ -1074,6 +1075,21 @@ def test_b910(self):
         ]
         self.assertEqual(errors, self.errors(*expected))
 
+    @unittest.skipIf(sys.version_info < (3, 13), "requires 3.13+")
+    def test_b911(self):
+        filename = Path(__file__).absolute().parent / "b911_py313.py"
+        bbc = BugBearChecker(filename=str(filename))
+        errors = list(bbc.run())
+        expected = [
+            B911(5, 0),
+            B911(6, 0),
+            B911(7, 0),
+            B911(8, 0),
+            B911(9, 0),
+            B911(10, 0),
+        ]
+        self.assertEqual(errors, self.errors(*expected))
+
 
 class TestFuzz(unittest.TestCase):
     from hypothesis import HealthCheck, given, settings