Merge pull request #389 from jcapriot/abstract_mat_truthiness

Implement truthiness for Zero and Identity

discretize/utils/matrix_utils.py

@@ -1493,6 +1493,10 @@ def __repr__(self):
         """Represent zeros a string."""
         return "Zero"
 
+    def __bool__(self):
+        """Return False for zero matrix."""
+        return False
+
     def __add__(self, v):
         """Add a value to zero."""
         return v
@@ -1655,6 +1659,10 @@ def __repr__(self):
         else:
             return "-I"
 
+    def __bool__(self):
+        """Return True for identity matrix."""
+        return True
+
     def __pos__(self):
         """Return positive 1 (or -1 if not positive)."""
         return self

tests/base/test_utils.py

@@ -273,6 +273,7 @@ def test_as_array_n_by_dim(self):
 class TestZero(unittest.TestCase):
     def test_zero(self):
         z = Zero()
+        assert not z
         assert z == 0
         assert not (z < 0)
         assert z <= 0
@@ -319,6 +320,7 @@ def test_numpy_multiply(self):
 
     def test_one(self):
         o = Identity()
+        assert o
         assert o == 1
         assert not (o < 1)
         assert o <= 1
@@ -411,6 +413,9 @@ def test_numpy_one(self):
     def test_both(self):
         z = Zero()
         o = Identity()
+        assert z or o
+        assert not (z and o)
+        assert o and not z
         assert o * z == 0
         assert o * z + o == 1
         assert o - z == 1