wjones127 commented on PR #14198:
URL: https://github.com/apache/arrow/pull/14198#issuecomment-1254350080
## Mapping MapType field names
```python
import pyarrow as pa
# MapType
ty_named = pa.map_(pa.field("x", pa.int32(), nullable=False), pa.int32())
ty = pa.map_(pa.int32(), pa.int32())
arr_named = pa.array([[(1, 2), (2, 4)]], type=ty_named)
arr_named.type, arr_named.cast(ty).type
```
**Before (wrong)**
```python
(MapType(map<int32 ('x'), int32>), MapType(map<int32 ('x'), int32>))
```
**After (correct)**
```python
(MapType(map<int32 ('x'), int32>), MapType(map<int32, int32>))
```
## Mapping Map<T, List<T>> names
```python
ty_named = pa.map_(pa.string(), pa.field("x", pa.list_(pa.field("x",
pa.int32(), nullable=True)), nullable=False))
ty = pa.map_(pa.string(), pa.list_(pa.int32()))
arr_named = pa.array([[("string", [1, 2, 3])]], type=ty_named)
arr_named.type, arr_named.cast(ty).type
```
**Before**
```python
pyarrow.lib.ArrowNotImplementedError: Unsupported cast from map<string,
list<x: int32> ('x')> to map<string, list<item: int32>> (no available cast
function for target type)
```
**After**
```python
(MapType(map<string, list<x: int32> ('x')>), MapType(map<string, list<item:
int32>>))
```
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