Add Image.array setter to avoid surprising results via numpy.array math operations

(#1272)

Author: rmjarvis

galsim/image.py

@@ -479,6 +479,10 @@ def iscontiguous(self):
         """
         return self._array.strides[1]//self._array.itemsize == 1
 
+    @array.setter
+    def array(self, other):
+        self._array[:] = self._safe_cast(other)
+
     @lazy_property
     def _image(self):
         cls = self._cpp_type[self.dtype]

tests/test_image.py

@@ -1734,6 +1734,19 @@ def test_Image_inplace_add():
                     err_msg="Inplace add in Image class does not match reference for dtypes = "
                     +str(types[i])+" and "+str(types[j]))
 
+        # Adding via array:
+        image4 = image2.copy()
+        image4.array += image2.array
+        np.testing.assert_allclose(image4.array, 2*image2.array)
+        image4.array[:] += image2.array
+        np.testing.assert_allclose(image4.array, 3*image2.array)
+        image4.array = image4.array + image2.array
+        np.testing.assert_allclose(image4.array, 4*image2.array)
+        with assert_raises(ValueError):
+            image4.array += image2.array[:2,:]
+        with assert_raises(ValueError):
+            image4.array = image4.array[:2,:] + image2.array[:2,:]
+
         with assert_raises(ValueError):
             image1 += image1.subImage(galsim.BoundsI(0,4,0,4))
 
@@ -1776,6 +1789,19 @@ def test_Image_inplace_subtract():
                     err_msg="Inplace subtract in Image class does not match reference for dtypes = "
                     +str(types[i])+" and "+str(types[j]))
 
+        # Subtracting via array:
+        image4 = 5*image2
+        image4.array -= image2.array
+        np.testing.assert_allclose(image4.array, 4*image2.array)
+        image4.array[:] -= image2.array
+        np.testing.assert_allclose(image4.array, 3*image2.array)
+        image4.array = image4.array - image2.array
+        np.testing.assert_allclose(image4.array, 2*image2.array)
+        with assert_raises(ValueError):
+            image4.array -= image2.array[:2,:]
+        with assert_raises(ValueError):
+            image4.array = image4.array[:2,:] - image2.array[:2,:]
+
         with assert_raises(ValueError):
             image1 -= image1.subImage(galsim.BoundsI(0,4,0,4))
 
@@ -1907,6 +1933,17 @@ def test_Image_inplace_scalar_add():
                 err_msg="Inplace scalar add in Image class does not match reference for dtype = "
                 +str(types[i]))
 
+        # Adding via array:
+        image4 = image1.copy()
+        image4.array += 1
+        np.testing.assert_allclose(image4.array, image1.array + 1)
+        image4.array[:] += 1
+        np.testing.assert_allclose(image4.array, image1.array + 2)
+        image4.array = image4.array + 1
+        np.testing.assert_allclose(image4.array, image1.array + 3)
+        with assert_raises(ValueError):
+            image4.array = image4.array[:2,:] + 1
+
 
 @timer
 def test_Image_inplace_scalar_subtract():
@@ -1961,6 +1998,17 @@ def test_Image_inplace_scalar_multiply():
                 err_msg="Inplace scalar multiply in Image class does"
                 +" not match reference for dtype = "+str(types[i]))
 
+        # Multiplying via array:
+        image4 = image2.copy()
+        image4.array *= 2
+        np.testing.assert_allclose(image4.array, 2*image2.array)
+        image4.array[:] *= 2
+        np.testing.assert_allclose(image4.array, 4*image2.array)
+        image4.array = image4.array * 2
+        np.testing.assert_allclose(image4.array, 8*image2.array)
+        with assert_raises(ValueError):
+            image4.array = image4.array[:2,:] * 2
+
 
 @timer
 def test_Image_inplace_scalar_divide():
@@ -1988,6 +2036,36 @@ def test_Image_inplace_scalar_divide():
                 err_msg="Inplace scalar divide in Image class does"
                 +" not match reference for dtype = "+str(types[i]))
 
+        # Dividing via array:
+        image4 = 16*image2
+        if simple_types[i] is int:
+            with assert_raises(TypeError):
+                image4.array /= 2
+            with assert_raises(TypeError):
+                image4.array[:] /= 2
+            np.testing.assert_array_equal(image4.array, 16*image2.array)  # unchanged yet
+            image4.array //= 2
+            np.testing.assert_array_equal(image4.array, 8*image2.array)
+            image4.array[:] //= 2
+            np.testing.assert_array_equal(image4.array, 4*image2.array)
+            image4.array = image4.array // 2
+            np.testing.assert_array_equal(image4.array, 2*image2.array)
+            # The following works for integer by explicitly rounding and casting.
+            # The native numpy operation would use floor to cast to int, which is 1 smaller.
+            image4.array = (image4.array / 2.0001)
+            np.testing.assert_array_equal(image4.array, image2.array)
+            with assert_raises(ValueError):
+                image4.array = image4.array[:2,:] // 2
+        else:
+            image4.array /= 2
+            np.testing.assert_allclose(image4.array, 8*image2.array)
+            image4.array[:] /= 2
+            np.testing.assert_allclose(image4.array, 4*image2.array)
+            image4.array = image4.array / 2
+            np.testing.assert_allclose(image4.array, 2*image2.array)
+            with assert_raises(ValueError):
+                image4.array = image4.array[:2,:] / 2
+
 
 @timer
 def test_Image_inplace_scalar_pow():