BUG: Fix regression in is_list_like

is_list_like() used to use isinstance(obj, abc.Iterable) before pandas-dev#39852 where it was optimized for performance. This resulted in a regression where objects that explicitly declare __iter__ as None are considered "list like" but not instances of abc.Iterable.

Author: aiudirog

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/libs/test_lib.py

@@ -206,3 +206,10 @@ def test_no_default_pickle():
     # GH#40397
     obj = tm.round_trip_pickle(lib.no_default)
     assert obj is lib.no_default
+
+
+def test_is_list_like_iter_is_none():
+    class NotListLike:
+        __iter__ = None
+
+    assert not lib.is_list_like(NotListLike())