Inspect arg as Python object, instead of using PyErr_Clear()

Tests/test_image_convert.py

@@ -225,6 +225,10 @@ def test_trns_RGB(tmp_path: Path) -> None:
     assert "transparency" not in im_p.info
     im_p.save(f)
 
+    im.info["transparency"] = list(im.info["transparency"])
+    im_rgba = im.convert("RGBA")
+    assert "transparency" not in im_rgba.info
+
     im = Image.new("RGB", (1, 1))
     im.info["transparency"] = im.getpixel((0, 0))
     im_p = im.convert("P", palette=Image.Palette.ADAPTIVE)
@@ -353,19 +357,24 @@ def test_matrix_xyz(mode: str) -> None:
 
 def test_matrix_identity() -> None:
     # Arrange
-    im = hopper("RGB")
+    im = hopper()
+    assert im.mode == "RGB"
+
     # fmt: off
     identity_matrix = (
         1, 0, 0, 0,
         0, 1, 0, 0,
         0, 0, 1, 0)
     # fmt: on
-    assert im.mode == "RGB"
 
     # Act
     # Convert with an identity matrix
-    converted_im = im.convert(mode="RGB", matrix=identity_matrix)
+    converted_im = im.convert("RGB", identity_matrix)
 
     # Assert
     # No change
     assert_image_equal(converted_im, im)
+
+    # Test list
+    converted_im = im.convert("RGB", list(identity_matrix))
+    assert_image_equal(converted_im, im)

src/PIL/Image.py

@@ -1017,7 +1017,7 @@ def verify(self) -> None:
     def convert(
         self,
         mode: str | None = None,
-        matrix: tuple[float, ...] | None = None,
+        matrix: list[float] | tuple[float, ...] | None = None,
         dither: Dither | None = None,
         palette: Palette = Palette.WEB,
         colors: int = 256,
@@ -1052,7 +1052,7 @@ def convert(
 
         :param mode: The requested mode. See: :ref:`concept-modes`.
         :param matrix: An optional conversion matrix.  If given, this
-           should be 4- or 12-tuple containing floating point values.
+           should be 4- or 12-sequence containing floating point values.
         :param dither: Dithering method, used when converting from
            mode "RGB" to "P" or from "RGB" or "L" to "1".
            Available methods are :data:`Dither.NONE` or :data:`Dither.FLOYDSTEINBERG`
@@ -1091,7 +1091,7 @@ def convert(
                 transparency = new_im.info["transparency"]
 
                 def convert_transparency(
-                    m: tuple[float, ...], v: tuple[int, int, int]
+                    m: list[float] | tuple[float, ...], v: tuple[int, int, int]
                 ) -> int:
                     value = m[0] * v[0] + m[1] * v[1] + m[2] * v[2] + m[3] * 0.5
                     return max(0, min(255, int(value)))

src/_imaging.c

@@ -1049,8 +1049,15 @@ static PyObject *
 _convert_matrix(ImagingObject *self, PyObject *args) {
     char *mode_name;
     float m[12];
-    if (!PyArg_ParseTuple(args, "s(ffff)", &mode_name, m + 0, m + 1, m + 2, m + 3)) {
-        PyErr_Clear();
+    PyObject *matrix;
+    if (!PyArg_ParseTuple(args, "sO", &mode_name, &matrix)) {
+        return NULL;
+    }
+    Py_ssize_t size = PySequence_Size(matrix);
+    if (size == -1) {
+        return NULL;
+    }
+    if (size == 12) {
         if (!PyArg_ParseTuple(
                 args,
                 "s(ffffffffffff)",
@@ -1070,27 +1077,35 @@ _convert_matrix(ImagingObject *self, PyObject *args) {
             )) {
             return NULL;
         }
+    } else if (!PyArg_ParseTuple(
+                   args, "s(ffff)", &mode_name, m + 0, m + 1, m + 2, m + 3
+               )) {
+        return NULL;
     }
 
     const ModeID mode = findModeID(mode_name);
-
     return PyImagingNew(ImagingConvertMatrix(self->image, mode, m));
 }
 
 static PyObject *
 _convert_transparent(ImagingObject *self, PyObject *args) {
     char *mode_name;
-    int r, g, b;
-    if (PyArg_ParseTuple(args, "s(iii)", &mode_name, &r, &g, &b)) {
-        const ModeID mode = findModeID(mode_name);
-        return PyImagingNew(ImagingConvertTransparent(self->image, mode, r, g, b));
+    int r, g = 0, b = 0;
+    PyObject *transparency;
+    if (!PyArg_ParseTuple(args, "sO", &mode_name, &transparency)) {
+        return NULL;
     }
-    PyErr_Clear();
-    if (PyArg_ParseTuple(args, "si", &mode_name, &r)) {
-        const ModeID mode = findModeID(mode_name);
-        return PyImagingNew(ImagingConvertTransparent(self->image, mode, r, 0, 0));
+
+    if (PySequence_Check(transparency)) {
+        if (!PyArg_ParseTuple(args, "s(iii)", &mode_name, &r, &g, &b)) {
+            return NULL;
+        }
+    } else if (!PyArg_ParseTuple(args, "si", &mode_name, &r)) {
+        return NULL;
     }
-    return NULL;
+
+    const ModeID mode = findModeID(mode_name);
+    return PyImagingNew(ImagingConvertTransparent(self->image, mode, r, g, b));
 }
 
 static PyObject *