Fix the rendering of Polars Struct

Author: mwouts

docs/changelog.md

@@ -1,8 +1,8 @@
 ITables ChangeLog
 =================
 
-2.4.0-dev
----------------------
+2.4.0 (2025-05-17)
+------------------
 
 **Added**
 - The ITable widget, and the ITable components for Dash and Streamlit have the same features as the `show` function. They can show non-finite floats, bigints, Pandas Style objects and use custom JavaScript formatters ([#374](https://github.com/mwouts/itables/issues/374))
@@ -18,6 +18,7 @@ ITables ChangeLog
 
 **Fixed**
 - We have added a new option `text_in_header_can_be_selected` (defaults to `True`). With that option the text in headers can be selected, giving you the option to select and copy the column names back to your Python code.
+- We have fixed the rendering of Polars Struct columns ([#290](https://github.com/mwouts/itables/issues/290))
 
 
 2.3.0 (2025-04-05)

src/itables/datatables_format.py

@@ -138,6 +138,19 @@ def datatables_rows(
         )
     except AttributeError:
         # Polars DataFrame
+        assert pl is not None
+
+        # Convert Polars Struct to string #290
+        if any(isinstance(df[col].dtype, pl.Struct) for col in df.columns):
+            columns = {col: df[col] for col in df.columns}
+            for col in df.columns:
+                if isinstance(df[col].dtype, pl.Struct):
+                    try:
+                        columns[col] = df[col].cast(str)
+                    except pl.exceptions.InvalidOperationError:
+                        columns[col] = [str(x) for x in df[col]]
+            df = pl.DataFrame(columns)
+
         data = df.rows()
         data = [[escape_non_finite_float(f) for f in row] for row in data]
 

src/itables/version.py

@@ -1,3 +1,3 @@
 """ITables' version number"""
 
-__version__ = "2.4.0-dev"
+__version__ = "2.4.0"

tests/test_polars.py

@@ -5,7 +5,7 @@
 from itables.sample_dfs import get_dict_of_test_dfs, get_dict_of_test_series
 
 try:
-    import polars  # noqa
+    import polars as pl  # noqa
 except ImportError as e:
     pytest.skip(str(e), allow_module_level=True)
 
@@ -26,7 +26,7 @@ def test_show_polars_df(name, df):
 
 def test_encode_mixed_contents():
     # Make sure that the bigint escape works for mixed content # 291
-    df = polars.DataFrame(
+    df = pl.DataFrame(
         {
             "bigint": [1666767918216000000],
             "int": [1699300000000],
@@ -38,3 +38,15 @@ def test_encode_mixed_contents():
         datatables_rows(df)
         == "[[1666767918216000000, 1699300000000, 0.9510565400123596, -0.30901700258255005]]"
     )
+
+
+def test_render_polars_struct():
+    df = pl.DataFrame(
+        {
+            "X": ["A", "A", "B", "C", "C", "C"],
+        }
+    )
+    assert (
+        datatables_rows(df.select(pl.col("X").value_counts(sort=True)))
+        == '[["{\\"C\\",3}"], ["{\\"A\\",2}"], ["{\\"B\\",1}"]]'
+    )