[Python] Casting Table to new schema ignores nullability of fields

[asfimport]

Similar to ARROW-15478, but not for nested fields but just for casting a full Table (in theory that could be the same code, but currently the Table.cast logic is implemented in cython).

So currently when casting a Table to a new schema, the nullability of the fields in the schema is ignored (and as a result you get an "invalid" schema indicating a field is non-nullable that actually can have nulls):

>>> table = pa.table({'a': [None, 1]})
>>> table
pyarrow.Table
a: int64
----
a: [[null,1]]

>>> new_schema = pa.schema([pa.field("a", "int64", nullable=False)])
>>> table.cast(new_schema)
pyarrow.Table
a: int64 not null
----
a: [[null,1]]

Reporter: Joris Van den Bossche / @jorisvandenbossche
Assignee: Kshiteej K / @kshitij12345

Related issues:

• [C++] Creating (or casting to) list array with non-nullable field doesn't check nulls (is related to)

PRs and other links:

• GitHub Pull Request #14048

_{Note: This issue was originally created as ARROW-16651. Please see the migration documentation for further details.}

[asfimport]

Joris Van den Bossche / @jorisvandenbossche:
Issue resolved by pull request 14048
#14048