Add new check - use-sequence-for-iteration

5 files changed, 49 insertions, 3 deletions

diff --git a/ChangeLog b/ChangeLog
index fae693a3d..ecfe42ff0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -118,6 +118,8 @@ Release date: TBA
 
   Closes #4828
 
+* Added ``use-sequence-for-iteration``: Emitted when iterating over an in-place defined ``set``.
+
 
 What's New in Pylint 2.9.6?
 ===========================
diff --git a/doc/whatsnew/2.10.rst b/doc/whatsnew/2.10.rst
index 585ac8cc7..d13099989 100644
--- a/doc/whatsnew/2.10.rst
+++ b/doc/whatsnew/2.10.rst
@@ -28,6 +28,8 @@ New checkers
 
   Closes #3692
 
+* Added ``use-sequence-for-iteration``: Emitted when iterating over an in-place defined ``set``.
+
 
 Other Changes
 =============
diff --git a/pylint/checkers/refactoring/recommendation_checker.py b/pylint/checkers/refactoring/recommendation_checker.py
index 252ae684a..b7bda5754 100644
--- a/pylint/checkers/refactoring/recommendation_checker.py
+++ b/pylint/checkers/refactoring/recommendation_checker.py
@@ -1,6 +1,6 @@
 # Licensed under the GPL: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
 # For details: https://github.com/PyCQA/pylint/blob/main/LICENSE
-from typing import cast
+from typing import Union, cast
 
 import astroid
 
@@ -43,6 +43,12 @@ class RecommendationChecker(checkers.BaseChecker):
             "str.split(sep, maxsplit=1)[0] or str.rsplit(sep, maxsplit=1)[-1] "
             "instead.",
         ),
+        "C0208": (
+            "Use a sequence type when iterating over values",
+            "use-sequence-for-iteration",
+            "When iterating over values, sequence types (e.g., ``lists``, ``tuples``, ``ranges``) "
+            "are more efficient than ``sets``.",
+        ),
     }
 
     @staticmethod
@@ -134,10 +140,15 @@ class RecommendationChecker(checkers.BaseChecker):
                 )
                 self.add_message("use-maxsplit-arg", node=node, args=(new_name,))
 
-    @utils.check_messages("consider-using-enumerate", "consider-using-dict-items")
+    @utils.check_messages(
+        "consider-using-enumerate",
+        "consider-using-dict-items",
+        "use-sequence-for-iteration",
+    )
     def visit_for(self, node: astroid.For) -> None:
         self._check_consider_using_enumerate(node)
         self._check_consider_using_dict_items(node)
+        self._check_use_sequence_for_iteration(node)
 
     def _check_consider_using_enumerate(self, node: astroid.For) -> None:
         """Emit a convention whenever range and len are used for indexing."""
@@ -262,9 +273,13 @@ class RecommendationChecker(checkers.BaseChecker):
                 self.add_message("consider-using-dict-items", node=node)
                 return
 
-    @utils.check_messages("consider-using-dict-items")
+    @utils.check_messages(
+        "consider-using-dict-items",
+        "use-sequence-for-iteration",
+    )
     def visit_comprehension(self, node: astroid.Comprehension) -> None:
         self._check_consider_using_dict_items_comprehension(node)
+        self._check_use_sequence_for_iteration(node)
 
     def _check_consider_using_dict_items_comprehension(
         self, node: astroid.Comprehension
@@ -291,3 +306,10 @@ class RecommendationChecker(checkers.BaseChecker):
 
                 self.add_message("consider-using-dict-items", node=node)
                 return
+
+    def _check_use_sequence_for_iteration(
+        self, node: Union[astroid.For, astroid.Comprehension]
+    ) -> None:
+        """Check if code iterates over an in-place defined set."""
+        if isinstance(node.iter, astroid.Set):
+            self.add_message("use-sequence-for-iteration", node=node.iter)
diff --git a/tests/functional/u/use/use_sequence_for_iteration.py b/tests/functional/u/use/use_sequence_for_iteration.py
new file mode 100644
index 000000000..2dd1feb18
--- /dev/null
+++ b/tests/functional/u/use/use_sequence_for_iteration.py
@@ -0,0 +1,16 @@
+# pylint: disable=missing-docstring,pointless-statement,unnecessary-comprehension
+
+var = {1, 2, 3}
+
+for x in var:
+    pass
+for x in {1, 2, 3}:  # [use-sequence-for-iteration]
+    pass
+
+(x for x in var)
+(x for x in {1, 2, 3})  # [use-sequence-for-iteration]
+
+[x for x in var]
+[x for x in {1, 2, 3}]  # [use-sequence-for-iteration]
+
+[x for x in {*var, 4}]  # [use-sequence-for-iteration]
diff --git a/tests/functional/u/use/use_sequence_for_iteration.txt b/tests/functional/u/use/use_sequence_for_iteration.txt
new file mode 100644
index 000000000..615df8a30
--- /dev/null
+++ b/tests/functional/u/use/use_sequence_for_iteration.txt
@@ -0,0 +1,4 @@
+use-sequence-for-iteration:7:9::Use a sequence type when iterating over values:HIGH
+use-sequence-for-iteration:11:12::Use a sequence type when iterating over values:HIGH
+use-sequence-for-iteration:14:12::Use a sequence type when iterating over values:HIGH
+use-sequence-for-iteration:16:12::Use a sequence type when iterating over values:HIGH