Make Numba an optional dependency

Signed-off-by: Beat Buesser <[email protected]>

Author: Beat Buesser

art/attacks/evasion/__init__.py

@@ -1,6 +1,8 @@
 """
 Module providing evasion attacks under a common interface.
 """
+import importlib
+
 from art.attacks.evasion.adversarial_patch.adversarial_patch import AdversarialPatch
 from art.attacks.evasion.adversarial_patch.adversarial_patch_numpy import AdversarialPatchNumpy
 from art.attacks.evasion.adversarial_patch.adversarial_patch_tensorflow import AdversarialPatchTensorFlowV2
@@ -9,7 +11,10 @@
 from art.attacks.evasion.adversarial_asr import CarliniWagnerASR
 from art.attacks.evasion.auto_attack import AutoAttack
 from art.attacks.evasion.auto_projected_gradient_descent import AutoProjectedGradientDescent
-from art.attacks.evasion.brendel_bethge import BrendelBethgeAttack
+
+if importlib.util.find_spec("numba") is not None:
+    from art.attacks.evasion.brendel_bethge import BrendelBethgeAttack
+
 from art.attacks.evasion.boundary import BoundaryAttack
 from art.attacks.evasion.carlini import CarliniL2Method, CarliniLInfMethod, CarliniL0Method
 from art.attacks.evasion.decision_tree_attack import DecisionTreeAttack

setup.py

@@ -13,7 +13,6 @@
     "six",
     "setuptools",
     "tqdm",
-    "numba>=0.53.1",
 ]
 
 docs_require = [
@@ -93,6 +92,7 @@ def get_version(rel_path):
             "cma",
             "librosa",
             "opencv-python",
+            "numba",
         ],
         "non_framework": [
             "matplotlib",
@@ -112,6 +112,7 @@ def get_version(rel_path):
             "codecov",
             "requests",
             "sortedcontainers",
+            "numba",
         ],
     },
     classifiers=[