Fix a false positive for consider-using-dict-items (#9594)

When iterating ``os.environ`` using the ``os.environ.keys()`` operation and then deleting an item using the key as a lookup.

Closes #9554

Co-authored-by: Pierre Sassoulas <[email protected]>>

doc/whatsnew/fragments/9554.false_positive

@@ -0,0 +1,3 @@
+Fix a false positive for ``consider-using-dict-items`` when iterating using ``keys()`` and then deleting an item using the key as a lookup.
+
+Closes #9554

pylint/checkers/refactoring/recommendation_checker.py

@@ -308,6 +308,10 @@ def _check_consider_using_dict_items(self, node: nodes.For) -> None:
                     # Ignore this subscript if it is the target of an assignment
                     # Early termination as dict index lookup is necessary
                     return
+                if isinstance(subscript.parent, nodes.Delete):
+                    # Ignore this subscript if the index is used to delete a
+                    # dictionary item.
+                    return
 
                 self.add_message("consider-using-dict-items", node=node)
                 return

tests/functional/c/consider/consider_using_dict_items.py

@@ -1,6 +1,10 @@
 """Emit a message for iteration through dict keys and subscripting dict with key."""
+
 # pylint: disable=line-too-long,missing-docstring,unsubscriptable-object,too-few-public-methods,redefined-outer-name,use-dict-literal,modified-iterating-dict
 
+import os
+
+
 def bad():
     a_dict = {1: 1, 2: 2, 3: 3}
     for k in a_dict:  # [consider-using-dict-items]
@@ -15,12 +19,15 @@ def good():
     for k in a_dict:
         print(k)
 
+
 out_of_scope_dict = dict()
 
+
 def another_bad():
     for k in out_of_scope_dict:  # [consider-using-dict-items]
         print(out_of_scope_dict[k])
 
+
 def another_good():
     for k in out_of_scope_dict:
         k = 1
@@ -47,9 +54,11 @@ def another_good():
 for k4 in b_dict.keys():  # [consider-iterating-dictionary,consider-using-dict-items]
     val = b_dict[k4]
 
+
 class Foo:
     c_dict = {}
 
+
 # Should emit warning when iterating over a dict attribute of a class
 for k5 in Foo.c_dict:  # [consider-using-dict-items]
     val = Foo.c_dict[k5]
@@ -88,18 +97,25 @@ class Foo:
 # Test false positive described in #4630
 # (https://github.com/pylint-dev/pylint/issues/4630)
 
-d = {'key': 'value'}
+d = {"key": "value"}
 
 for k in d:  # this is fine, with the reassignment of d[k], d[k] is necessary
-    d[k] += '123'
-    if '1' in d[k]:  # index lookup necessary here, do not emit error
-        print('found 1')
+    d[k] += "123"
+    if "1" in d[k]:  # index lookup necessary here, do not emit error
+        print("found 1")
 
 for k in d:  # if this gets rewritten to d.items(), we are back to the above problem
     d[k] = d[k] + 1
-    if '1' in d[k]:  # index lookup necessary here, do not emit error
-        print('found 1')
+    if "1" in d[k]:  # index lookup necessary here, do not emit error
+        print("found 1")
 
 for k in d:  # [consider-using-dict-items]
-    if '1' in d[k]:  # index lookup necessary here, do not emit error
-        print('found 1')
+    if "1" in d[k]:  # index lookup necessary here, do not emit error
+        print("found 1")
+
+
+# False positive in issue #9554
+# https://github.com/pylint-dev/pylint/issues/9554
+for var in os.environ.keys():  # [consider-iterating-dictionary]
+    if var.startswith("foo_"):
+        del os.environ[var]  # index lookup necessary here, do not emit error

tests/functional/c/consider/consider_using_dict_items.txt

@@ -1,16 +1,17 @@
-consider-using-dict-items:6:4:7:24:bad:Consider iterating with .items():UNDEFINED
-consider-using-dict-items:9:4:10:30:bad:Consider iterating with .items():UNDEFINED
-consider-using-dict-items:21:4:22:35:another_bad:Consider iterating with .items():UNDEFINED
-consider-using-dict-items:40:0:42:18::Consider iterating with .items():UNDEFINED
-consider-using-dict-items:44:0:45:20::Consider iterating with .items():UNDEFINED
-consider-iterating-dictionary:47:10:47:23::Consider iterating the dictionary directly instead of calling .keys():INFERENCE
-consider-using-dict-items:47:0:48:20::Consider iterating with .items():UNDEFINED
-consider-using-dict-items:54:0:55:24::Consider iterating with .items():UNDEFINED
-consider-using-dict-items:67:0:None:None::Consider iterating with .items():UNDEFINED
-consider-using-dict-items:68:0:None:None::Consider iterating with .items():UNDEFINED
-consider-using-dict-items:71:0:None:None::Consider iterating with .items():UNDEFINED
-consider-using-dict-items:72:0:None:None::Consider iterating with .items():UNDEFINED
-consider-using-dict-items:75:0:None:None::Consider iterating with .items():UNDEFINED
-consider-iterating-dictionary:86:25:86:42::Consider iterating the dictionary directly instead of calling .keys():INFERENCE
-consider-using-dict-items:86:0:None:None::Consider iterating with .items():UNDEFINED
-consider-using-dict-items:103:0:105:24::Consider iterating with .items():UNDEFINED
+consider-using-dict-items:10:4:11:24:bad:Consider iterating with .items():UNDEFINED
+consider-using-dict-items:13:4:14:30:bad:Consider iterating with .items():UNDEFINED
+consider-using-dict-items:27:4:28:35:another_bad:Consider iterating with .items():UNDEFINED
+consider-using-dict-items:47:0:49:18::Consider iterating with .items():UNDEFINED
+consider-using-dict-items:51:0:52:20::Consider iterating with .items():UNDEFINED
+consider-iterating-dictionary:54:10:54:23::Consider iterating the dictionary directly instead of calling .keys():INFERENCE
+consider-using-dict-items:54:0:55:20::Consider iterating with .items():UNDEFINED
+consider-using-dict-items:63:0:64:24::Consider iterating with .items():UNDEFINED
+consider-using-dict-items:76:0:None:None::Consider iterating with .items():UNDEFINED
+consider-using-dict-items:77:0:None:None::Consider iterating with .items():UNDEFINED
+consider-using-dict-items:80:0:None:None::Consider iterating with .items():UNDEFINED
+consider-using-dict-items:81:0:None:None::Consider iterating with .items():UNDEFINED
+consider-using-dict-items:84:0:None:None::Consider iterating with .items():UNDEFINED
+consider-iterating-dictionary:95:25:95:42::Consider iterating the dictionary directly instead of calling .keys():INFERENCE
+consider-using-dict-items:95:0:None:None::Consider iterating with .items():UNDEFINED
+consider-using-dict-items:112:0:114:24::Consider iterating with .items():UNDEFINED
+consider-iterating-dictionary:119:11:119:28::Consider iterating the dictionary directly instead of calling .keys():INFERENCE