Merge pull request #4835 from cdce8p/feature-sequence_for_iteration

Add `use-sequence-for-iteration` checker

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?
 ===========================

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
 =============

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 @@ def _check_use_maxsplit_arg(self, node: astroid.Call) -> None:
                 )
                 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."""
@@ -262,8 +273,18 @@ def _check_consider_using_dict_items(self, node: astroid.For) -> None:
                 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
+    ) -> None:
+        """Add message when accessing dict values by index lookup."""
         iterating_object_name = utils.get_iterating_dictionary_name(node)
         if iterating_object_name is None:
             return
@@ -285,3 +306,10 @@ def visit_comprehension(self, node: astroid.Comprehension) -> None:
 
                 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)

tests/functional/ext/code_style/code_style_consider_using_tuple.py

@@ -12,7 +12,7 @@
 (x for x in var)
 (x for x in (1, 2, 3))
 (x for x in [1, 2, 3])  # [consider-using-tuple]
-(x for x in {1, 2, 3})  # [consider-using-tuple]
+(x for x in {1, 2, 3})  # [consider-using-tuple,use-sequence-for-iteration]
 
 [x for x in var]
 [x for x in (1, 2, 3)]
@@ -26,4 +26,4 @@
     pass
 
 [x for x in [*var, 2]]
-[x for x in {*var, 2}]
+[x for x in {*var, 2}]  # [use-sequence-for-iteration]

tests/functional/ext/code_style/code_style_consider_using_tuple.txt

@@ -1,4 +1,6 @@
 consider-using-tuple:9:9::Consider using an in-place tuple instead of list
 consider-using-tuple:14:12::Consider using an in-place tuple instead of list
 consider-using-tuple:15:12::Consider using an in-place tuple instead of set
+use-sequence-for-iteration:15:12::Use a sequence type when iterating over values
 consider-using-tuple:19:12::Consider using an in-place tuple instead of list
+use-sequence-for-iteration:29:12::Use a sequence type when iterating over values

tests/functional/u/undefined/undefined_loop_variable.py

@@ -44,7 +44,7 @@ def do_stuff_with_a_list():
 
 
 def do_stuff_with_a_set():
-    for var in {1, 2, 3}:
+    for var in {1, 2, 3}:  # pylint: disable=use-sequence-for-iteration
         pass
     return var
 

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]

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