Make _make_linear_lut public and issue deprecation warnings from old private methods

PIL/ImagePalette.py

@@ -17,6 +17,7 @@
 #
 
 import array
+import warnings
 from PIL import Image, ImageColor
 
 
@@ -125,6 +126,26 @@ def raw(rawmode, data):
 # Factories
 
 def _make_linear_lut(black, white):
+    warnings.warn(
+        '_make_linear_lut() is deprecated. '
+        'Please call make_linear_lut() instead.',
+        DeprecationWarning,
+        stacklevel=2
+    )
+    return make_linear_lut(black, white)
+
+
+def _make_gamma_lut(exp):
+    warnings.warn(
+        '_make_gamma_lut() is deprecated. '
+        'Please call make_gamma_lut() instead.',
+        DeprecationWarning,
+        stacklevel=2
+    )
+    return make_gamma_lut(exp)
+
+
+def make_linear_lut(black, white):
     lut = []
     if black == 0:
         for i in range(256):

Tests/test_imagepalette.py

@@ -44,6 +44,34 @@ class TestImagePalette(PillowTestCase):
         self.assertIsInstance(p, ImagePalette)
         self.assertEqual(p.palette, palette.tobytes())
 
+    def test_make_linear_lut(self):
+        # Arrange
+        from PIL.ImagePalette import make_linear_lut
+        black = 0
+        white = 255
+
+        # Act
+        lut = make_linear_lut(black, white)
+
+        # Assert
+        self.assertIsInstance(lut, list)
+        self.assertEqual(len(lut), 256)
+        # Check values
+        for i in range(0, len(lut)):
+            self.assertEqual(lut[i], i)
+
+    def test_make_linear_lut_not_yet_implemented(self):
+        # Update after FIXME
+        # Arrange
+        from PIL.ImagePalette import make_linear_lut
+        black = 1
+        white = 255
+
+        # Act
+        self.assertRaises(
+            NotImplementedError,
+            lambda: make_linear_lut(black, white))
+
     def test_make_gamma_lut(self):
         # Arrange
         from PIL.ImagePalette import make_gamma_lut
@@ -62,6 +90,27 @@ class TestImagePalette(PillowTestCase):
         self.assertEqual(lut[191], 60)
         self.assertEqual(lut[255], 255)
 
+    def test_private_make_linear_lut_warning(self):
+        # Arrange
+        from PIL.ImagePalette import _make_linear_lut
+        black = 0
+        white = 255
+
+        # Act / Assert
+        self.assert_warning(
+            DeprecationWarning,
+            lambda: _make_linear_lut(black, white))
+
+    def test_private_make_gamma_lut_warning(self):
+        # Arrange
+        from PIL.ImagePalette import _make_gamma_lut
+        exp = 5
+
+        # Act / Assert
+        self.assert_warning(
+            DeprecationWarning,
+            lambda: _make_gamma_lut(exp))
+
 
 if __name__ == '__main__':
     unittest.main()