Merge pull request #557 from aleju/fix_seed

Fix random.seed not always seeding in-place

changelogs/master/fixed/20200110_fixed_seed.md

@@ -0,0 +1,8 @@
+# Fixed `random.seed` not always seeding in-place #557
+
+Fixed `imgaug.random.seed()` not seeding the global `RNG` in-place
+in numpy 1.17+. The (unfixed) function instead created a new
+global `RNG` with the given seed. This set the seed of augmenters
+created *after* the `seed()` call, but not of augmenters created
+*before* the `seed()` call as they would continue to use the old
+global RNG.

imgaug/random.py

@@ -868,10 +868,11 @@ def seed(entropy):
 
 
 def _seed_np117_(entropy):
-    # pylint: disable=global-statement
-    global GLOBAL_RNG
-    # TODO any way to seed the Generator object instead of creating a new one?
-    GLOBAL_RNG = RNG(entropy)
+    # We can't easily seed a BitGenerator in-place, nor can we easily modify
+    # a Generator's bit_generator in-place. So instead we create a new
+    # bit generator and set the current global RNG's internal bit generator
+    # state to a copy of the new bit generator's state.
+    get_global_rng().state = BIT_GENERATOR(entropy).state
 
 
 def _seed_np116_(entropy):

test/test_random.py

@@ -18,6 +18,7 @@
 import numpy as np
 
 import imgaug as ia
+import imgaug.augmenters as iaa
 from imgaug.testutils import reseed
 import imgaug.random as iarandom
 
@@ -704,6 +705,44 @@ def test_integrationtest(self):
         iarandom.seed(1)
         assert iarandom.GLOBAL_RNG.equals(iarandom.RNG(1))
 
+    def test_seed_affects_augmenters_created_after_its_call(self):
+        image = np.full((50, 50, 3), 128, dtype=np.uint8)
+
+        images_aug = []
+        for _ in np.arange(5):
+            iarandom.seed(100)
+            aug = iaa.AdditiveGaussianNoise(scale=50, per_channel=True)
+            images_aug.append(aug(image=image))
+
+        # assert all images identical
+        for other_image_aug in images_aug[1:]:
+            assert np.array_equal(images_aug[0], other_image_aug)
+
+        # but different seed must lead to different image
+        iarandom.seed(101)
+        aug = iaa.AdditiveGaussianNoise(scale=50, per_channel=True)
+        image_aug = aug(image=image)
+        assert not np.array_equal(images_aug[0], image_aug)
+
+    def test_seed_affects_augmenters_created_before_its_call(self):
+        image = np.full((50, 50, 3), 128, dtype=np.uint8)
+
+        images_aug = []
+        for _ in np.arange(5):
+            aug = iaa.AdditiveGaussianNoise(scale=50, per_channel=True)
+            iarandom.seed(100)
+            images_aug.append(aug(image=image))
+
+        # assert all images identical
+        for other_image_aug in images_aug[1:]:
+            assert np.array_equal(images_aug[0], other_image_aug)
+
+        # but different seed must lead to different image
+        aug = iaa.AdditiveGaussianNoise(scale=50, per_channel=True)
+        iarandom.seed(101)
+        image_aug = aug(image=image)
+        assert not np.array_equal(images_aug[0], image_aug)
+
 
 class Test_normalize_generator(_Base):
     @mock.patch("imgaug.random.normalize_generator_")