delegate Image.mode and Image.size to the values on Image.im when available

When setting the values on Image also try to update the values on Image.im. There isn't currently a way to update values in the other direction.

Tests/test_image.py

@@ -662,7 +662,7 @@ class TestImage:
         blank_pa.palette = None
 
         def _make_new(base_image, im, palette_result=None):
-            new_im = base_image._new(im)
+            new_im = base_image._new(im.im)
             assert new_im.mode == im.mode
             assert new_im.size == im.size
             assert new_im.info == base_image.info

src/PIL/GifImagePlugin.py

@@ -328,8 +328,8 @@ class GifImageFile(ImageFile.ImageFile):
                         self._mode = "RGBA"
                         del self.info["transparency"]
                     else:
-                        self._mode = "RGB"
                         self.im = self.im.convert("RGB", Image.Dither.FLOYDSTEINBERG)
+                        self._mode = "RGB"
 
         def _rgb(color):
             if self._frame_palette:

src/PIL/IcnsImagePlugin.py

@@ -261,11 +261,7 @@ class IcnsImageFile(ImageFile.ImageFile):
             self.best_size[1] * self.best_size[2],
         )
 
-    @property
+    @Image.Image.size.setter
-    def size(self):
-        return self._size
-
-    @size.setter
     def size(self, value):
         info_size = value
         if info_size not in self.info["sizes"] and len(info_size) == 2:
@@ -283,7 +279,10 @@ class IcnsImageFile(ImageFile.ImageFile):
         if info_size not in self.info["sizes"]:
             msg = "This is not one of the allowed sizes of this image"
             raise ValueError(msg)
-        self._size = value
+        if value != self.size:
+            self.im = None
+            self.pyaccess = None
+            self._size = value
 
     def load(self):
         if len(self.size) == 3:
@@ -306,7 +305,7 @@ class IcnsImageFile(ImageFile.ImageFile):
 
         self.im = im.im
         self._mode = im.mode
-        self.size = im.size
+        self._size = im.size
 
         return px
 

src/PIL/IcoImagePlugin.py

@@ -310,36 +310,36 @@ class IcoImageFile(ImageFile.ImageFile):
         self.size = self.ico.entry[0]["dim"]
         self.load()
 
-    @property
+    @Image.Image.size.setter
-    def size(self):
-        return self._size
-
-    @size.setter
     def size(self, value):
         if value not in self.info["sizes"]:
             msg = "This is not one of the allowed sizes of this image"
             raise ValueError(msg)
-        self._size = value
+        if value != self.size:
+            self.im = None
+            self.pyaccess = None
+            self._size = value
 
     def load(self):
         if self.im is not None and self.im.size == self.size:
             # Already loaded
             return Image.Image.load(self)
-        im = self.ico.getimage(self.size)
+        size_to_load = self.size
+        im = self.ico.getimage(size_to_load)
         # if tile is PNG, it won't really be loaded yet
         im.load()
         self.im = im.im
         self.pyaccess = None
         self._mode = im.mode
-        if im.size != self.size:
+        if im.size != size_to_load:
             warnings.warn("Image was not the expected size")
 
-            index = self.ico.getentryindex(self.size)
+            index = self.ico.getentryindex(size_to_load)
             sizes = list(self.info["sizes"])
             sizes[index] = im.size
             self.info["sizes"] = set(sizes)
 
-            self.size = im.size
+            self._size = im.size
 
     def load_seek(self):
         # Flag the ImageFile.Parser so that it

src/PIL/Image.py

@@ -480,16 +480,21 @@ class Image:
 
     def __init__(self):
         # FIXME: take "new" parameters / other image?
-        # FIXME: turn mode and size into delegating properties?
         self.im = None
-        self._mode = ""
+        # do not directly change __mode; use _mode instead
-        self._size = (0, 0)
+        self.__mode = ""
+        # do not directly change __size; use _size instead
+        self.__size = (0, 0)
         self.palette = None
         self.info = {}
         self.readonly = 0
         self.pyaccess = None
         self._exif = None
 
+    def _use_im_values(self):
+        ''' Whether or not to try using values from self.im in addition to the values in this class. '''
+        return self.im is not None
+
     @property
     def width(self):
         return self.size[0]
@@ -502,10 +507,36 @@ class Image:
     def size(self):
         return self._size
 
+    @property
+    def _size(self):
+        if self._use_im_values():
+            return self.im.size
+        return self.__size
+
+    @_size.setter
+    def _size(self, value):
+        # set im.size first in case it raises an excepton
+        if self._use_im_values():
+            self.im.size = value
+        self.__size = value
+
     @property
     def mode(self):
         return self._mode
 
+    @property
+    def _mode(self):
+        if self._use_im_values():
+            return self.im.mode
+        return self.__mode
+
+    @_mode.setter
+    def _mode(self, value):
+        # set im.mode first in case it raises an excepton
+        if self._use_im_values():
+            self.im.mode = value
+        self.__mode = value
+
     def _new(self, im):
         new = Image()
         new.im = im

src/PIL/ImageFile.py

@@ -139,6 +139,9 @@ class ImageFile(Image.Image):
         if self.format is not None:
             return Image.MIME.get(self.format.upper())
 
+    def _use_im_values(self):
+        return self.tile is None and self.im is not None
+
     def __setstate__(self, state):
         self.tile = []
         super().__setstate__(state)

src/_imaging.c

@@ -3646,11 +3646,49 @@ _getattr_mode(ImagingObject *self, void *closure) {
     return PyUnicode_FromString(self->image->mode);
 }
 
+static int
+_setattr_mode(ImagingObject *self, PyObject *value, void *closure) {
+    if (value == NULL) {
+        self->image->mode[0] = '\0';
+        return 0;
+    }
+
+    const char *mode = PyUnicode_AsUTF8(value);
+    if (mode == NULL) {
+        return -1;
+    }
+    if (strlen(mode) >= IMAGING_MODE_LENGTH) {
+        PyErr_SetString(PyExc_ValueError, "given mode name is too long");
+        return -1;
+    }
+
+    strcpy(self->image->mode, mode);
+    return 0;
+}
+
 static PyObject *
 _getattr_size(ImagingObject *self, void *closure) {
     return Py_BuildValue("ii", self->image->xsize, self->image->ysize);
 }
 
+static int
+_setattr_size(ImagingObject *self, PyObject *value, void *closure) {
+    if (value == NULL) {
+        self->image->xsize = 0;
+        self->image->ysize = 0;
+        return 0;
+    }
+
+    int xsize, ysize;
+    if (!PyArg_ParseTuple(value, "ii", &xsize, &ysize)) {
+        return -1;
+    }
+
+    self->image->xsize = xsize;
+    self->image->ysize = ysize;
+    return 0;
+}
+
 static PyObject *
 _getattr_bands(ImagingObject *self, void *closure) {
     return PyLong_FromLong(self->image->bands);
@@ -3679,13 +3717,14 @@ _getattr_unsafe_ptrs(ImagingObject *self, void *closure) {
 };
 
 static struct PyGetSetDef getsetters[] = {
-    {"mode", (getter)_getattr_mode},
+    {"mode", (getter)_getattr_mode, (setter)_setattr_mode},
-    {"size", (getter)_getattr_size},
+    {"size", (getter)_getattr_size, (setter)_setattr_size},
     {"bands", (getter)_getattr_bands},
     {"id", (getter)_getattr_id},
     {"ptr", (getter)_getattr_ptr},
     {"unsafe_ptrs", (getter)_getattr_unsafe_ptrs},
-    {NULL}};
+    {NULL}
+};
 
 /* basic sequence semantics */