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https://issues.apache.org/jira/browse/ARROW-12609?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sergey Mozharov updated ARROW-12609:
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Summary: TypeError when accessing length of an invalid ListScalar (was:
TypeError when accessing length of a ListScalar with list-like data type)
> TypeError when accessing length of an invalid ListScalar
> --------------------------------------------------------
>
> Key: ARROW-12609
> URL: https://issues.apache.org/jira/browse/ARROW-12609
> Project: Apache Arrow
> Issue Type: Bug
> Components: Python
> Affects Versions: 3.0.0, 4.0.0
> Environment: Windows 10
> python=3.9.2
> pyarrow=4.0.0 (3.0.0 has the same behavior)
> Reporter: Sergey Mozharov
> Priority: Major
>
> For List-like data types, the scalar type corresponding to a missing value
> has '___len___' attribute, but TypeError is raised when it is accessed
> {code:java}
> import pyarrow as pa
> 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()
> {code}
> 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:
> {code:java}
> import pyarrow as pa
> 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
> {code}
> In this second example the TypeError is not raised.
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