new model system

models/util.py

@@ -0,0 +1,12 @@
+import random
+
+
+class Bernoulli(object):
+    def __init__(self, percentage):
+        self.percentage = percentage
+
+    def rand(self):
+        return random.random() < self.percentage
+
+    def random(self):
+        return self.rand()