pi-lens/rules/tree-sitter-queries/python/iter-return-iterator.yml

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# __iter__ Should Return Iterator
# Detects __iter__ methods that don't return an iterator
id: iter-return-iterator
name: __iter__ Should Return Iterator
severity: warning
category: reliability
defect_class: correctness
inline_tier: blocking
language: python

message: "__iter__ should return an iterator (object with __next__ method)"

description: |
  The __iter__ method must return an iterator object (something with a __next__ method).
  Returning a non-iterator will cause TypeError when iterating.

  ✅ FIX: Return self (if class has __next__) or use iter() on a collection

  ```python
  class MyIterator:
      def __iter__(self):
          return self  # OK - self has __next__
      
      def __next__(self):
          return 1

  class MyCollection:
      def __iter__(self):
          return iter(self.items)  # OK - returns iterator
  ```

query: |
  (function_definition
    name: (identifier) @NAME (#eq? @NAME "__iter__")
    body: (block
      (return_statement) @RETURN))

metavars:
  - NAME
  - RETURN

tags:
  - reliability
  - python-specific
  - iterator
  - protocol

examples:
  bad: |
    class MyClass:
        def __iter__(self):
            return [1, 2, 3]  # BAD - returns list, not iterator

  good: |
    class MyClass:
        def __iter__(self):
            return iter([1, 2, 3])  # GOOD - returns iterator

has_fix: false