BUG: Fix regression in is_list_like (#43373)

Author: aiudirog

doc/source/whatsnew/v1.3.3.rst

@@ -20,6 +20,7 @@ Fixed regressions
 - Fixed regression in :meth:`merge` where ``on`` columns with ``ExtensionDtype`` or ``bool`` data types were cast to ``object`` in ``right`` and ``outer`` merge (:issue:`40073`)
 - Fixed regression in :meth:`RangeIndex.where` and :meth:`RangeIndex.putmask` raising ``AssertionError`` when result did not represent a :class:`RangeIndex` (:issue:`43240`)
 - Fixed regression in :meth:`read_parquet` where the ``fastparquet`` engine would not work properly with fastparquet 0.7.0 (:issue:`43075`)
+- Fixed regression in :func:`is_list_like` where objects with ``__iter__`` set to ``None`` would be identified as iterable (:issue:`43373`)
 
 .. ---------------------------------------------------------------------------
 

pandas/_libs/lib.pyx

@@ -1092,7 +1092,7 @@ def is_list_like(obj: object, allow_sets: bool = True) -> bool:
 cdef inline bint c_is_list_like(object obj, bint allow_sets) except -1:
     return (
         # equiv: `isinstance(obj, abc.Iterable)`
-        hasattr(obj, "__iter__") and not isinstance(obj, type)
+        getattr(obj, "__iter__", None) is not None and not isinstance(obj, type)
         # we do not count strings/unicode/bytes as list-like
         and not isinstance(obj, (str, bytes))
         # exclude zero-dimensional numpy arrays, effectively scalars

pandas/tests/dtypes/test_inference.py

@@ -150,6 +150,18 @@ def foo():
         foo()
 
 
+def test_is_list_like_iter_is_none():
+    # GH 43373
+    # is_list_like was yielding false positives with __iter__ == None
+    class NotListLike:
+        def __getitem__(self, item):
+            return self
+
+        __iter__ = None
+
+    assert not inference.is_list_like(NotListLike())
+
+
 def test_is_sequence():
     is_seq = inference.is_sequence
     assert is_seq((1, 2))