rok commented on code in PR #47147:
URL: https://github.com/apache/arrow/pull/47147#discussion_r2263984852
##########
python/pyarrow/pandas_compat.py:
##########
@@ -275,11 +275,14 @@ def construct_metadata(columns_to_convert, df,
column_names, index_levels,
else:
index_descriptors = index_column_metadata = column_indexes = []
+ attributes: dict = df.attrs if df.attrs else {}
Review Comment:
Can attrs actually be None? The [NDframe
constructor](https://github.com/pandas-dev/pandas/blame/c888af6d0bb674932007623c0867e1fbd4bdc2c6/pandas/core/generic.py#L282)
I fround seems to say it'll always be a dict, maybe with values. If this is
indeed true (I might be wrong) we could just have:
```suggestion
attributes = df.attrs
```
If older versions of pandas don't have `attrs` would be safer:
```python
attributes = df.attrs if hasattr(df, "attrs") else {}
```
Note: type annotations are coming, but we're not sure they'll be inline or
not. So I'd suggest not adding it here.
##########
python/pyarrow/tests/parquet/test_pandas.py:
##########
@@ -101,6 +101,33 @@ def
test_merging_parquet_tables_with_different_pandas_metadata(tempdir):
writer.write_table(table2)
+@pytest.mark.pandas
+def test_attributes_metadata_persistence(tempdir):
+ # GH-45382: Add support for pandas DataFrame.attrs
+ # During the .parquet file writing, the attrs are serialised into json
+ # along with the rest of the pandas.DataFrame metadata.
+
+ filename = tempdir / "metadata_persistence.parquet"
+ df = alltypes_sample(size=10000)
+ df.attrs = {
+ 'float16': 'half-precision',
+ 'float32': 'single precision',
+ 'float64': 'double precision',
+ 'desciption': 'Attributes Persistence Test DataFrame',
+ }
+
+ table = pa.Table.from_pandas(df)
+ assert b'attributes' in table.schema.metadata[b'pandas']
+
+ _write_table(table, filename)
+ metadata = pq.read_metadata(filename).metadata
+ assert b'attributes' in table.schema.metadata[b'pandas']
Review Comment:
Since we're not chnanging schemas metadata (as far as I can tell), one of
these asserts is redundant:
```python
assert b'attributes' in table.schema.metadata[b'pandas']
```
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