Expose registered file extensions in Image

PIL/Image.py

@@ -2512,6 +2512,16 @@ def register_extension(id, extension):
     EXTENSION[extension.lower()] = id.upper()
 
 
+def registered_extensions():
+    """
+    Returns a dictionary containing all file extensions belonging
+    to registered plugins
+    """
+    if not bool(EXTENSION):
+        init()
+    return EXTENSION
+
+
 # --------------------------------------------------------------------
 # Simple display support.  User code may override this.
 

Tests/test_image.py

@@ -196,6 +196,35 @@ def test_alpha_composite(self):
         img_colors = sorted(img.getcolors())
         self.assertEqual(img_colors, expected_colors)
 
+    def test_registered_extensions_uninitialized(self):
+        # Arrange
+        Image._initialized = 0
+        extension = Image.EXTENSION
+        Image.EXTENSION = {}
+
+        # Act
+        Image.registered_extensions()
+
+        # Assert
+        self.assertEqual(Image._initialized, 2)
+
+        # Restore the original state and assert
+        Image.EXTENSION = extension
+        self.assertTrue(Image.EXTENSION)
+
+    def test_registered_extensions(self):
+        # Arrange
+        # Open an image to trigger plugin registration
+        Image.open('Tests/images/rgb.jpg')
+
+        # Act
+        extensions = Image.registered_extensions()
+
+        # Assert
+        self.assertTrue(bool(extensions))
+        for ext in ['.cur', '.icns', '.tif', '.tiff']:
+            self.assertIn(ext, extensions)
+
     def test_effect_mandelbrot(self):
         # Arrange
         size = (512, 512)