undefined-variable can now find undefined loop iterables

Close #498

ChangeLog

@@ -29,6 +29,10 @@ Release date: TBA
 
    Close #3301
 
+* ``undefined-variable`` can now find undefined loop iterables
+
+   Close #498
+
 * ``safe_infer`` can infer a value as long as all the paths share the same type.
 
   Close #2503

pylint/checkers/variables.py

@@ -546,7 +546,7 @@ def mark_as_consumed(self, name, new_node):
         del self.to_consume[name]
 
     def get_next_to_consume(self, node):
-        # mark the name as consumed if it's defined in this scope
+        # Get the definition of `node` from this scope
         name = node.name
         parent_node = node.parent
         found_node = self.to_consume.get(name)
@@ -558,6 +558,14 @@ def get_next_to_consume(self, node):
             lhs = found_node[0].parent.targets[0]
             if lhs.name == name:  # this name is defined in this very statement
                 found_node = None
+
+        if (
+            found_node
+            and isinstance(parent_node, astroid.For)
+            and parent_node.iter == node
+            and parent_node.target in found_node
+        ):
+            found_node = None
         return found_node
 
 

tests/functional/u/undefined_variable.py

@@ -274,3 +274,10 @@ def func_should_fail(_dt: datetime):  # [used-before-assignment]
 def tick(counter: Counter, name: str, dictionary: OrderedDict) -> OrderedDict:
     counter[name] += 1
     return dictionary
+
+
+# pylint: disable=unused-argument
+def not_using_loop_variable_accordingly(iterator):
+    for iteree in iteree: # [undefined-variable]
+        yield iteree
+# pylint: enable=unused-argument

tests/functional/u/undefined_variable.txt

@@ -25,3 +25,4 @@ undefined-variable:170::Undefined variable 'unicode_3'
 undefined-variable:225:LambdaClass4.<lambda>:Undefined variable 'LambdaClass4'
 undefined-variable:233:LambdaClass5.<lambda>:Undefined variable 'LambdaClass5'
 used-before-assignment:254:func_should_fail:Using variable 'datetime' before assignment
+undefined-variable:281:not_using_loop_variable_accordingly:Undefined variable 'iteree'