fix(python): Truncate long column name in glimpse (#8281)

py-polars/polars/dataframe/frame.py

@@ -3544,6 +3544,7 @@ def glimpse(self, *, return_as_string: bool = False) -> str | None:
         # always print at most this number of values, mainly used to ensure
         # we do not cast long arrays to strings which would be very slow
         max_num_values = min(10, self.height)
+        max_col_name_trunc = 50
 
         def _parse_column(col_name: str, dtype: PolarsDataType) -> tuple[str, str, str]:
             dtype_str = (
@@ -3553,6 +3554,8 @@ def _parse_column(col_name: str, dtype: PolarsDataType) -> tuple[str, str, str]:
             )
             val = self[:max_num_values][col_name].to_list()
             val_str = ", ".join(map(str, val))
+            if len(col_name) > max_col_name_trunc:
+                col_name = col_name[: (max_col_name_trunc - 3)] + "..."
             return col_name, dtype_str, val_str
 
         data = [_parse_column(s, dtype) for s, dtype in self.schema.items()]

py-polars/tests/unit/test_df.py

@@ -3407,6 +3407,18 @@ def test_glimpse(capsys: Any) -> None:
     # remove the last newline on the capsys
     assert capsys.readouterr().out[:-1] == expected
 
+    colc = "a" * 96
+    df = pl.DataFrame({colc: [11, 22, 33]})
+    result = df.glimpse(return_as_string=True)
+    expected = textwrap.dedent(
+        """\
+        Rows: 3
+        Columns: 1
+        $ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa... <i64> 11, 22, 33
+        """
+    )
+    assert result == expected
+
 
 def test_item() -> None:
     df = pl.DataFrame({"a": [1]})