Add use-set-for-membership check

ChangeLog

@@ -147,6 +147,11 @@ Release date: TBA
 
   * Emit ``consider-using-tuple`` even if list contains a ``starred`` expression.
 
+  * Added ``use-set-for-membership``: Emitted when using an in-place defined ``list``
+    or ``tuple`` to do a membership test. ``sets`` are better optimized for that.
+
+    Closes #4776
+
 * Ignore decorators lines by similarities checker when ignore signatures flag enabled
 
   Closes #4839

doc/whatsnew/2.10.rst

@@ -44,6 +44,11 @@ Extensions
 
   * Emit ``consider-using-tuple`` even if list contains a ``starred`` expression.
 
+  * Added ``use-set-for-membership``: Emitted when using an in-place defined ``list``
+    or ``tuple`` to do a membership test. ``sets`` are better optimized for that.
+
+    Closes #4776
+
 
 Other Changes
 =============

pylint/extensions/code_style.py

@@ -41,6 +41,12 @@ class CodeStyleChecker(BaseChecker):
             "Emitted where an in-place defined ``list`` can be replaced by a ``tuple``. "
             "Due to optimizations by CPython, there is no performance benefit from it.",
         ),
+        "R6103": (
+            "Consider using set for membership test",
+            "use-set-for-membership",
+            "Membership tests are more efficient when performed on "
+            "a lookup optimized datatype like ``sets``.",
+        ),
     }
 
     def __init__(self, linter: PyLinter) -> None:
@@ -59,6 +65,12 @@ def visit_for(self, node: nodes.For) -> None:
     def visit_comprehension(self, node: nodes.Comprehension) -> None:
         self._check_inplace_defined_list(node)
 
+    @check_messages("use-set-for-membership")
+    def visit_compare(self, node: nodes.Compare) -> None:
+        for op, comparator in node.ops:
+            if op == "in":
+                self._check_in_comparison(comparator)
+
     def _check_dict_consider_namedtuple_dataclass(self, node: nodes.Dict) -> None:
         """Check if dictionary values can be replaced by Namedtuple or Dataclass."""
         if not (
@@ -140,6 +152,14 @@ def _check_inplace_defined_list(
         if isinstance(node.iter, nodes.List):
             self.add_message("consider-using-tuple", node=node.iter)
 
+    def _check_in_comparison(self, comparator: nodes.NodeNG) -> None:
+        """Checks for membership comparisons with in-place container objects."""
+        if not isinstance(comparator, nodes._BaseContainer):
+            return
+
+        if not isinstance(comparator, nodes.Set):
+            self.add_message("use-set-for-membership", node=comparator)
+
 
 def register(linter: PyLinter) -> None:
     linter.register_checker(CodeStyleChecker(linter))

tests/functional/ext/code_style/code_style_use_set_membership.py

@@ -0,0 +1,33 @@
+# pylint: disable=invalid-name,missing-docstring,pointless-statement,unnecessary-comprehension
+
+x = 1
+var = frozenset({1, 2, 3})
+
+x in var
+x in {1, 2, 3}
+x in (1, 2, 3)  # [use-set-for-membership]
+x in [1, 2, 3]  # [use-set-for-membership]
+
+if x in var:
+    pass
+if x in {1, 2, 3}:
+    pass
+if x in (1, 2, 3):  # [use-set-for-membership]
+    pass
+if x in [1, 2, 3]:  # [use-set-for-membership]
+    pass
+
+x in {*var}
+x in (*var,)  # [use-set-for-membership]
+x in [*var]  # [use-set-for-membership]
+
+42 if x in [1, 2, 3] else None  # [use-set-for-membership]
+assert x in [1, 2, 3]  # [use-set-for-membership]
+(x for x in var if x in [1, 2, 3])  # [use-set-for-membership]
+while x in [1, 2, 3]:  # [use-set-for-membership]
+    break
+
+# Stacked operators, rightmost pair is evaluated first
+# Doesn't make much sense in practice since `in` will only return `bool`
+True == x in [1, 2, 3]  # [use-set-for-membership]  # noqa: E712
+1 >= x in [1, 2, 3]  # [use-set-for-membership]  # noqa: E712

tests/functional/ext/code_style/code_style_use_set_membership.rc

@@ -0,0 +1,2 @@
+[MASTER]
+load-plugins=pylint.extensions.code_style

tests/functional/ext/code_style/code_style_use_set_membership.txt

@@ -0,0 +1,12 @@
+use-set-for-membership:8:5::Consider using set for membership test:HIGH
+use-set-for-membership:9:5::Consider using set for membership test:HIGH
+use-set-for-membership:15:8::Consider using set for membership test:HIGH
+use-set-for-membership:17:8::Consider using set for membership test:HIGH
+use-set-for-membership:21:5::Consider using set for membership test:HIGH
+use-set-for-membership:22:5::Consider using set for membership test:HIGH
+use-set-for-membership:24:11::Consider using set for membership test:HIGH
+use-set-for-membership:25:12::Consider using set for membership test:HIGH
+use-set-for-membership:26:24::Consider using set for membership test:HIGH
+use-set-for-membership:27:11::Consider using set for membership test:HIGH
+use-set-for-membership:32:13::Consider using set for membership test:HIGH
+use-set-for-membership:33:10::Consider using set for membership test:HIGH