added tests to cover save of four different png transparencies

Tests/test_file_png.py

@@ -128,6 +128,34 @@ def test_load_transparent_p():
     # image has 124 uniqe qlpha values
     assert_equal(len(im.split()[3].getcolors()), 124)
 
+def test_save_p_transparent_palette():
+    in_file = "Tests/images/pil123p.png"
+    im = Image.open(in_file)
+
+    file = tempfile("temp.png")
+    assert_no_exception(lambda: im.save(file))
+
+def test_save_p_single_transparency():
+    in_file = "Tests/images/p_trns_single.png"
+    im = Image.open(in_file)
+
+    file = tempfile("temp.png")
+    assert_no_exception(lambda: im.save(file))
+
+def test_save_l_transparency():
+    in_file = "Tests/images/l_trns.png"
+    im = Image.open(in_file)
+
+    file = tempfile("temp.png")
+    assert_no_exception(lambda: im.save(file))
+
+def test_save_rgb_single_transparency():
+    in_file = "Tests/images/caption_6_33_22.png"
+    im = Image.open(in_file)
+
+    file = tempfile("temp.png")
+    assert_no_exception(lambda: im.save(file))
+
 def test_load_verify():
     # Check open/load/verify exception (@PIL150)
 

_imaging.c

@@ -742,16 +742,16 @@ _convert(ImagingObject* self, PyObject* args)
     ImagingObject *paletteimage = NULL;
 
     if (!PyArg_ParseTuple(args, "s|iO", &mode, &dither, &paletteimage))
-    return NULL;
+      return NULL;
     if (paletteimage != NULL) {
       if (!PyImaging_Check(paletteimage)) {
-    PyObject_Print((PyObject *)paletteimage, stderr, 0);
-    PyErr_SetString(PyExc_ValueError, "palette argument must be image with mode 'P'");
-    return NULL;
+        PyObject_Print((PyObject *)paletteimage, stderr, 0);
+        PyErr_SetString(PyExc_ValueError, "palette argument must be image with mode 'P'");
+        return NULL;
       }
       if (paletteimage->image->palette == NULL) {
-    PyErr_SetString(PyExc_ValueError, "null palette");
-    return NULL;
+        PyErr_SetString(PyExc_ValueError, "null palette");
+        return NULL;
       }
     }
 
@@ -1431,16 +1431,16 @@ _putpalettealpha(ImagingObject* self, PyObject* args)
     int index;
     int alpha = 0;
     if (!PyArg_ParseTuple(args, "i|i", &index, &alpha))
-    return NULL;
+        return NULL;
 
     if (!self->image->palette) {
-    PyErr_SetString(PyExc_ValueError, no_palette);
-    return NULL;
+        PyErr_SetString(PyExc_ValueError, no_palette);
+        return NULL;
     }
 
     if (index < 0 || index >= 256) {
-    PyErr_SetString(PyExc_ValueError, outside_palette);
-    return NULL;
+        PyErr_SetString(PyExc_ValueError, outside_palette);
+        return NULL;
     }
 
     strcpy(self->image->palette->mode, "RGBA");