[
https://issues.apache.org/jira/browse/ARROW-12609?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Sergey Mozharov updated ARROW-12609:
------------------------------------
Description:
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.
was:
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.
> 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: 3.0.0, 4.0.0
> Environment: 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
> ```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.
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