explode series after slide fast path (#3467)

pola-rs · May 22, 2022 · 4a39576 · 4a39576
1 parent 5c128e3
commit 4a39576
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Showing 3 changed files with 13 additions and 2 deletions.
diff --git a/polars/polars-core/src/frame/explode.rs b/polars/polars-core/src/frame/explode.rs
@@ -52,7 +52,13 @@ impl DataFrame {
                 if !ca.can_fast_explode() {
                     let (_, offsets) = get_exploded(col)?;
                     if offsets.is_empty() {
-                        return Ok(self.slice(0, 0));
+                        let mut out = self.slice(0, 0);
+                        // still explode the columns to get the inner dtype
+                        for col in &columns {
+                            out.try_apply(col.name(), |s| s.explode())?;
+                        }
+
+                        return Ok(out);
                     }
 
                     let mut mask = MutableBitmap::from_len_set(offsets.len() - 1);

diff --git a/py-polars/src/file.rs b/py-polars/src/file.rs
@@ -212,7 +212,7 @@ pub fn get_either_file(py_f: PyObject, truncate: bool) -> PyResult<EitherRustPyt
         } else {
             match File::open(str_slice) {
                 Ok(file) => BufReader::new(file),
-                Err(e) => {
+                Err(_e) => {
                     return Err(PyErr::new::<PyFileNotFoundError, _>(format!(
                         "No such file or directory: {}",
                         str_slice

diff --git a/py-polars/tests/test_explode.py b/py-polars/tests/test_explode.py
@@ -6,3 +6,8 @@
 def test_explode_empty_df_3402() -> None:
     df = pl.DataFrame({"a": pa.array([], type=pa.large_list(pa.int32()))})
     assert df.explode("a").dtypes == [pl.Int32]
+
+
+def test_explode_empty_df_3460() -> None:
+    df = pl.DataFrame({"a": pa.array([[]], type=pa.large_list(pa.int32()))})
+    assert df.explode("a").dtypes == [pl.Int32]