Fix pylint-dev#5608: Emit redefined-outer-name for redefinitions of loop variables in body

Author: jacobtylerwalls

.copyrite_aliases

@@ -113,5 +113,10 @@
     "mails": ["[email protected]", "[email protected]"],
     "authoritative_mail": "[email protected]",
     "name": "Tushar Sadhwani"
+  },
+  {
+    "mails": ["[email protected]"],
+    "authoritative_mail": "[email protected]",
+    "name": "Jacob Walls"
   }
 ]

ChangeLog

@@ -124,6 +124,11 @@ Release date: TBA
   Closes #4434
   Closes #5370
 
+* Emit ``redefined-outer-name`` when a loop variable is redefined in the loop
+  body. Previously, only redefinitions taking place in nested loops were flagged.
+
+  Closes #5608
+
 * ``encoding`` can now be supplied as a positional argument to calls that open
   files without triggering ``unspecified-encoding``.
 

doc/whatsnew/2.13.rst

@@ -127,6 +127,11 @@ Other Changes
   Closes #4434
   Closes #5370
 
+* Emit ``redefined-outer-name`` when a loop variable is redefined in the loop
+  body. Previously, only redefinitions taking place in nested loops were flagged.
+
+  Closes #5608
+
 * ``encoding`` can now be supplied as a positional argument to calls that open
   files without triggering ``unspecified-encoding``.
 

pylint/checkers/variables.py

@@ -482,9 +482,10 @@ def _has_locals_call_after_node(stmt, scope):
         "`'from X import *'` style import.",
     ),
     "W0621": (
-        "Redefining name %r from outer scope (line %s)",
+        "Redefining name %r from outer scope or loop (line %s)",
         "redefined-outer-name",
-        "Used when a variable's name hides a name defined in the outer scope.",
+        "Used when a variable's name hides a name defined in an outer scope, "
+        "for loop, or except handler.",
     ),
     "W0622": (
         "Redefining built-in %r",
@@ -740,7 +741,7 @@ class VariablesChecker(BaseChecker):
     """checks for
     * unused variables / imports
     * undefined variables
-    * redefinition of variable from builtins or from an outer scope
+    * redefinition of variable from builtins or from an outer scope, for loop, or except handler
     * use of variable before assignment
     * __all__ consistency
     * self/cls assignment
@@ -1112,6 +1113,17 @@ def visit_global(self, node: nodes.Global) -> None:
             self.add_message("global-statement", node=node)
 
     def visit_assignname(self, node: nodes.AssignName) -> None:
+        if self.linter.is_message_enabled("redefined-outer-name") and isinstance(node.parent, nodes.Assign):
+            for outer_for, outer_variables in self._loop_variables:
+                if node.name in outer_variables and not in_for_else_branch(
+                    outer_for, node
+                ):
+                    self.add_message(
+                        "redefined-outer-name",
+                        args=(node.name, outer_for.fromlineno),
+                        node=node,
+                    )
+                    break
         if isinstance(node.assign_type(), nodes.AugAssign):
             self.visit_name(node)
 

tests/functional/b/bad_indentation.py

@@ -13,6 +13,7 @@ def titii():
 
 def tataa(kdict):
     for key in ['1', '2', '3']:
+        # pylint: disable=redefined-outer-name
         key = key.lower()
 
         if key in kdict:

tests/functional/c/cellvar_escaping_loop.py

@@ -76,7 +76,7 @@ def good_case10():
     lst = []
     for i in range(10):  # pylint: disable=unused-variable
         def func():
-            i = 100
+            i = 100  # pylint: disable=redefined-outer-name
             def func2(arg=i):
                 return arg
 

tests/functional/r/redefined_loop_name.py

@@ -0,0 +1,15 @@
+"""Tests for redefinitions of loop variables inside the loop body.
+
+See: https://github.com/PyCQA/pylint/issues/5608
+"""
+# pylint: disable=invalid-name
+
+lines = ["1\t", "2\t"]
+for line in lines:
+    line = line.strip()  # [redefined-outer-name]
+
+lines = [(1, "1\t"), (2, "2\t")]
+for i, line in lines:
+    line = line.strip()  # [redefined-outer-name]
+
+line = "no warning"

tests/functional/r/redefined_loop_name.txt

@@ -0,0 +1,2 @@
+redefined-outer-name:9:4:9:8::Redefining name 'line' from outer scope (line 8):UNDEFINED
+redefined-outer-name:13:4:13:8::Redefining name 'line' from outer scope (line 12):UNDEFINED

tests/functional/u/undefined/undefined_loop_variable.py

@@ -21,7 +21,7 @@ def do_else(some_random_list):
 VAR2 = B # nor this one
 
 for var1, var2 in TEST_LC:
-    var1 = var2 + 4
+    var1 = var2 + 4  # pylint: disable=redefined-outer-name
 VAR3 = var1 # [undefined-loop-variable]
 
 for note in __revision__:

tests/functional/u/unnecessary/unnecessary_dict_index_lookup.py

@@ -12,7 +12,7 @@
 
 for k, v in b_dict.items():
     print(k)
-    k = "another key"
+    k = "another key"  # pylint: disable=redefined-outer-name
     print(b_dict[k])  # This is fine, key reassigned
 
 
@@ -68,7 +68,7 @@ class Foo:
 for item in d.items():
     print(item[0])
     print(d[item[0]])  # [unnecessary-dict-index-lookup]
-    item = (2, "b")
+    item = (2, "b")  # pylint: disable=redefined-outer-name
     print(d[item[0]])  # This is fine, no warning thrown as key has been reassigned
 
 

tests/nested.py

@@ -0,0 +1,4 @@
+for x in range(10):
+  for x in range(10):
+    pass
+

tests/test.py

@@ -0,0 +1,3 @@
+for y in range(2):
+  y = None
+