Sergey Mozharov created ARROW-12609: ---------------------------------------
Summary: TypeError when accessing length of a ListScalar with list-like data type Key: ARROW-12609 URL: https://issues.apache.org/jira/browse/ARROW-12609 Project: Apache Arrow Issue Type: Bug Components: Python Affects Versions: 4.0.0, 3.0.0 Environment: python=3.9.2 pyarrow=4.0.0 (3.0.0 has the same behavior) Reporter: Sergey Mozharov For List-like data types, the scalar type corresponding to a missing value has '__len__' attribute, but TypeError is raised when it is accessed ```python data_type = pa.list_(pa.struct([ ('a', pa.int64()), ('b', pa.bool_()) ])) data = [[\{'a': 1, 'b': False}, \{'a': 2, 'b': True}], None] arr = pa.array(data, type=data_type) missing_scalar = arr[1] # <pyarrow.ListScalar: None> assert hasattr(missing_scalar, '__len__') assert len(missing_scalar) == 0 # --> TypeError: object of type 'NoneType' has no len() ``` Expected behavior: length is expected to be 0. This issue causes several pandas unit tests to fail when an ExtensionArray backed by arrow array with this data type is built. This behavior is also inconsistent with a similar example where the data type is a struct: ```python data_type = pa.struct([ ('a', pa.int64()), ('b', pa.bool_()) ]) data = [\{'a': 1, 'b': False}, None] arr = pa.array(data, type=data_type) missing_scalar = arr[1] # <pyarrow.StructScalar: None> assert hasattr(missing_scalar, '__len__') assert len(missing_scalar) == 0 # Ok ``` In this second example the TypeError is not raised. -- This message was sent by Atlassian Jira (v8.3.4#803005)