[GitHub] [arrow] pitrou commented on pull request #8312: ARROW-9941: [Python] Better string representation for extension types

[GitBox <gi...@apache.org>]

pitrou commented on pull request #8312:
URL: https://github.com/apache/arrow/pull/8312#issuecomment-702017880


   The problem is that this won't be visible from C++ code, which will still get `extension<arrow.py_extension_type>`.
   ```python
   >>> ty
   IntegerType(DataType(int64))
   >>> pa.DataType.__str__(ty)
   'extension<arrow.py_extension_type>'
   ```
   
   Solving this requires some collaboration with the C++ side.  I advise you to take a look at [`cpp/src/arrow/python/extension_type.h`](https://github.com/apache/arrow/blob/master/cpp/src/arrow/python/extension_type.h). You'll probably need to override the `ToString` method in `arrow::py::PyExtensionType`. By default it can return the same as `ExtensionType::ToString`, but it can also query a Python attribute on `type_instance` to get a custom string.


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