GH-39579: [Python] fix raising ValueError on _ensure_partitioning (#3…

…9593)

### Rationale for this change
The `_ensure_partitioning` method in dataset.py is missing a "raise" which currently ignores bad scheme silently.

### What changes are included in this PR?

Fixed the typo.

### Are these changes tested?
Tried with new code that the exception is properly raised.

### Are there any user-facing changes?
No.

* Closes: #39579

Lead-authored-by: idailylife <[email protected]>
Co-authored-by: 0x0000ffff <[email protected]>
Co-authored-by: Alenka Frim <[email protected]>
Signed-off-by: AlenkaF <[email protected]>

python/pyarrow/dataset.py

@@ -292,8 +292,8 @@ def _ensure_partitioning(scheme):
     elif isinstance(scheme, (Partitioning, PartitioningFactory)):
         pass
     else:
-        ValueError("Expected Partitioning or PartitioningFactory, got {}"
-                   .format(type(scheme)))
+        raise ValueError("Expected Partitioning or PartitioningFactory, got {}"
+                         .format(type(scheme)))
     return scheme
 
 

python/pyarrow/tests/test_dataset.py

@@ -701,6 +701,17 @@ def test_partitioning():
             load_back_table = load_back.to_table()
             assert load_back_table.equals(table)
 
+    # test invalid partitioning input
+    with tempfile.TemporaryDirectory() as tempdir:
+        partitioning = ds.DirectoryPartitioning(partitioning_schema)
+        ds.write_dataset(table, tempdir,
+                         format='ipc', partitioning=partitioning)
+        load_back = None
+        with pytest.raises(ValueError,
+                           match="Expected Partitioning or PartitioningFactory"):
+            load_back = ds.dataset(tempdir, format='ipc', partitioning=int(0))
+        assert load_back is None
+
 
 def test_partitioning_pickling(pickle_module):
     schema = pa.schema([