[ARROW-12695] [Python] bool value of scalars depends on data type

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 4.0.0
• Component/s: Python
• Environment: Windows 10 ; python 3.9.4
• External issue URL: https://github.com/apache/arrow/issues/28440
• Assignee: Unassigned
• Reporter: Sergey Mozharov
• Created: 08/May/21 00:31
• Updated: 11/Jan/23 08:28

Description

`pyarrow.Scalar` and its subclasses do not implement `_bool_` method. The default implementation does not seem to do the right thing. For example:

>>> import pyarrow as pa
>>> na_value = pa.scalar(None, type=pa.int32())
>>> bool(na_value)
True
>>> na_value = pa.scalar(None, type=pa.struct([('a', pa.int32())]))
>>> bool(na_value)
False
>>> bool(pa.scalar(None, type=pa.list_(pa.int32())))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "pyarrow\scalar.pxi", line 572, in pyarrow.lib.ListScalar.__len__
TypeError: object of type 'NoneType' has no len()
>>>

Please consider implementing `__bool__` method. It seems reasonable to delegate to the `__bool__` method of the wrapped object.