Add a discrete syntactic sugar for rv_discrete.

src/distributions.py

@@ -711,3 +711,13 @@ def __init__(self, *args, **kwargs):
         pk = [1./len(xk)] * len(xk)
         kwargs['values'] = (xk, pk)
         super().__init__(*args, **kwargs)
+
+class discrete(rv_discrete):
+    def __init__(self, *args, **kwargs):
+        assert len(args) == 1
+        assert not kwargs
+        values = args[0]
+        xk = tuple(values.keys())
+        pk = tuple(values.values())
+        kwargs['values'] = (xk, pk)
+        super().__init__(**kwargs)

tests/test_parse_distributions.py

@@ -8,6 +8,7 @@
 from spn.distributions import DistributionMix
 from spn.distributions import bernoulli
 from spn.distributions import choice
+from spn.distributions import discrete
 from spn.distributions import norm
 from spn.distributions import poisson
 from spn.distributions import rv_discrete
@@ -48,12 +49,15 @@ def test_error():
         a(X)
 
 def test_parse_rv_discrete():
-    dist = rv_discrete(values=((1, 2, 10), (.3, .5, .2)))
-    spn = dist(X)
-    assert allclose(spn.prob(X<<{1}), .3)
-    assert allclose(spn.prob(X<<{2}), .5)
-    assert allclose(spn.prob(X<<{10}), .2)
-    assert allclose(spn.prob(X<=10), 1)
+    for dist in [
+        rv_discrete(values=((1, 2, 10), (.3, .5, .2))),
+        discrete({1: .3, 2: .5, 10: .2})
+    ]:
+        spn = dist(X)
+        assert allclose(spn.prob(X<<{1}), .3)
+        assert allclose(spn.prob(X<<{2}), .5)
+        assert allclose(spn.prob(X<<{10}), .2)
+        assert allclose(spn.prob(X<=10), 1)
 
     dist = uniformd(values=((1, 2, 10, 0)))
     spn = dist(X)