fix(python): validate BFloat16.from_bytes length

python/python/tests/test_arrow.py

@@ -48,6 +48,16 @@ def test_bf16_value():
     assert not any(comparison for comparison in should_be_false)
 
 
+def test_bf16_from_bytes_roundtrip():
+    assert BFloat16.from_bytes(b"\xc0\x3f") == BFloat16(1.5)
+
+
+@pytest.mark.parametrize("bad", [b"", b"\x00", b"\x00\x00\x00", b"\x00" * 4])
+def test_bf16_from_bytes_invalid_length_raises(bad):
+    with pytest.raises(ValueError, match="expected 2 bytes"):
+        BFloat16.from_bytes(bad)
+
+
 def test_bf16_repr():
     data = [1.1, None, 3.4]
     arr = bfloat16_array(data)

python/src/arrow.rs

@@ -36,10 +36,10 @@ impl BFloat16 {
     #[classmethod]
     fn from_bytes(_cls: &Bound<'_, PyType>, bytes: &[u8]) -> PyResult<Self> {
         if bytes.len() != 2 {
-            PyValueError::new_err(format!(
+            return Err(PyValueError::new_err(format!(
                 "BFloat16::from_bytes: expected 2 bytes, got {}",
                 bytes.len()
-            ));
+            )));
         }
         Ok(Self(bf16::from_bits(u16::from_ne_bytes([
             bytes[0], bytes[1],