fix[python]: fix json_path_match dtype (#4915)

polars/polars-lazy/src/physical_plan/executors/filter.rs

@@ -26,7 +26,11 @@ impl Executor for FilterExec {
         }
         let df = self.input.execute(state)?;
         let s = self.predicate.evaluate(&df, state)?;
-        let mask = s.bool().expect("filter predicate wasn't of type boolean");
+        let mask = s.bool().map_err(|e| {
+            PolarsError::ComputeError(
+                format!("Filter predicate must be of type Boolean, got: {:?}", e).into(),
+            )
+        })?;
 
         let profile_name = if state.has_node_timer() {
             Cow::Owned(format!(".filter({})", &self.predicate.as_ref()))

py-polars/src/lazy/dsl.rs

@@ -729,7 +729,7 @@ impl PyExpr {
         };
         self.clone()
             .inner
-            .map(function, GetOutput::from_type(DataType::Boolean))
+            .map(function, GetOutput::from_type(DataType::Utf8))
             .with_fmt("str.json_path_match")
             .into()
     }

py-polars/tests/unit/test_errors.py

@@ -187,3 +187,11 @@ def test_error_on_double_agg() -> None:
 def test_unique_on_list_df() -> None:
     with pytest.raises(pl.InvalidOperationError):
         pl.DataFrame({"a": [1, 2, 3, 4], "b": [[1, 1], [2], [3], [4, 4]]}).unique()
+
+
+def test_filter_not_of_type_bool() -> None:
+    df = pl.DataFrame({"json_val": ['{"a":"hello"}', None, '{"a":"world"}']})
+    with pytest.raises(
+        pl.ComputeError, match="Filter predicate must be of type Boolean, got"
+    ):
+        df.filter(pl.col("json_val").str.json_path_match("$.a"))

py-polars/tests/unit/test_utf8.py

@@ -5,3 +5,10 @@ def test_min_max_agg_on_str() -> None:
     strings = ["b", "a", "x"]
     s = pl.Series(strings)
     assert (s.min(), s.max()) == ("a", "x")
+
+
+def test_json_path_match_type_4905() -> None:
+    df = pl.DataFrame({"json_val": ['{"a":"hello"}', None, '{"a":"world"}']})
+    assert df.filter(
+        pl.col("json_val").str.json_path_match("$.a").is_in(["hello"])
+    ).to_dict(False) == {"json_val": ['{"a":"hello"}']}