[jira] [Created] (ARROW-18430) [Python] Cannot cast nested nullable field to not-nullable

["&res (Jira)" <ji...@apache.org>]

&res created ARROW-18430:
----------------------------

             Summary: [Python] Cannot cast nested nullable field to not-nullable
                 Key: ARROW-18430
                 URL: https://issues.apache.org/jira/browse/ARROW-18430
             Project: Apache Arrow
          Issue Type: Improvement
          Components: Python
    Affects Versions: 10.0.1
            Reporter: &res


Casting from nullable field to not-nullable works provided all values are present. So for example this is a valid cast:
{code:java}
table = pa.table({'column_1': pa.array([1, 2 ,3])})table.cast(
    pa.schema([
        f.with_nullable(False) for f in table.schema
    ])
){code}
But it doesn't work for nested field. Here's an example:
{code:java}
import pyarrow as pa

record = {"nested_int": 1}

data_type = pa.struct(
    [
        pa.field("nested_int", pa.int32(), nullable=True),
    ]
)

data_type_after = pa.struct(
    [
        pa.field("nested_int", pa.int32(), nullable=False),
    ]
)

table = pa.table({"column_1": pa.array([record], data_type)})

table.cast(pa.schema([pa.field("column_1", data_type_after)])) {code}
Throws:
{code:java}
pyarrow.lib.ArrowTypeError: cannot cast nullable field to non-nullable field: struct<nested_int: int32> struct<nested_int: int32 not null> {code}
This is somewhat related to [https://github.com/apache/arrow/issues/13177] and https://issues.apache.org/jira/browse/ARROW-16603 



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