Cosmetics

nifty5/minimization/energy.py

@@ -131,24 +131,24 @@ class Energy(NiftyMetaBase()):
 
     def __mul__(self, factor):
         from .energy_sum import EnergySum
-        if not isinstance(factor, (float, int)):
-            raise TypeError("Factor must be a real-valued scalar")
-        return EnergySum.make([self], [factor])
+        if isinstance(factor, (float, int)):
+            return EnergySum.make([self], [factor])
+        return NotImplemented
 
     def __rmul__(self, factor):
         return self.__mul__(factor)
 
     def __add__(self, other):
         from .energy_sum import EnergySum
-        if not isinstance(other, Energy):
-            raise TypeError("can only add Energies to Energies")
-        return EnergySum.make([self, other])
+        if isinstance(other, Energy):
+            return EnergySum.make([self, other])
+        return NotImplemented
 
     def __sub__(self, other):
         from .energy_sum import EnergySum
-        if not isinstance(other, Energy):
-            raise TypeError("can only subtract Energies from Energies")
-        return EnergySum.make([self, other], [1., -1.])
+        if isinstance(other, Energy):
+            return EnergySum.make([self, other], [1., -1.])
+        return NotImplemented
 
     def __neg__(self):
         from .energy_sum import EnergySum

nifty5/minimization/energy_sum.py

@@ -16,8 +16,8 @@
 # NIFTy is being developed at the Max-Planck-Institut fuer Astrophysik
 # and financially supported by the Studienstiftung des deutschen Volkes.
 
-from .energy import Energy
 from ..utilities import memo
+from .energy import Energy
 
 
 class EnergySum(Energy):

test/test_energies/test_energy_sum.py

@@ -16,11 +16,12 @@
 # NIFTy is being developed at the Max-Planck-Institut fuer Astrophysik
 # and financially supported by the Studienstiftung des deutschen Volkes.
 
-import nifty5 as ift
-import numpy as np
 import unittest
 from itertools import product
 from test.common import expand
+
+import nifty5 as ift
+import numpy as np
 from numpy.testing import assert_allclose, assert_raises