Added common check for size tuple errors

PIL/Image.py

@@ -1985,6 +1985,22 @@ def _wedge():
 
     return Image()._new(core.wedge("L"))
 
+def _check_size(size):
+    """
+    Common check to enforce type and sanity check on size tuples
+
+    :param size: Should be a 2 tuple of (width, height)
+    :returns: True, or raises a ValueError
+    """
+
+    if not isinstance(size, tuple):
+        raise ValueError("Size must be a tuple")
+    if len(size) != 2:
+        raise ValueError("Size must be a tuple of length 2")
+    if size[0] <= 0 or size[1] <= 0:
+        raise ValueError("Width and Height must be > 0")
+
+    return True
 
 def new(mode, size, color=0):
     """
@@ -2002,6 +2018,8 @@ def new(mode, size, color=0):
     :returns: An :py:class:`~PIL.Image.Image` object.
     """
 
+    _check_size(size)
+    
     if color is None:
         # don't initialize
         return Image()._new(core.new(mode, size))
@@ -2039,6 +2057,8 @@ def frombytes(mode, size, data, decoder_name="raw", *args):
     :returns: An :py:class:`~PIL.Image.Image` object.
     """
 
+    _check_size(size)
+
     # may pass tuple instead of argument list
     if len(args) == 1 and isinstance(args[0], tuple):
         args = args[0]
@@ -2091,6 +2111,8 @@ def frombuffer(mode, size, data, decoder_name="raw", *args):
     .. versionadded:: 1.1.4
     """
 
+    _check_size(size)
+
     # may pass tuple instead of argument list
     if len(args) == 1 and isinstance(args[0], tuple):
         args = args[0]

Tests/test_image.py

@@ -237,5 +237,17 @@ class TestImage(PillowTestCase):
         im3 = Image.open('Tests/images/effect_spread.png')
         self.assert_image_similar(im2, im3, 110)
 
+    def test_check_size(self):
+        # Checking that the _check_size function throws value errors when we want it to. 
+        with self.assertRaises(ValueError):
+            Image.new('RGB', 0)  # not a tuple
+        with self.assertRaises(ValueError):
+            Image.new('RGB', (0,))  # Tuple too short
+        with self.assertRaises(ValueError):
+            Image.new('RGB', (0,0))  # w,h <= 0
+
+        self.assertTrue(Image.new('RGB', (1,1)))
+            
+
 if __name__ == '__main__':
     unittest.main()