minor clean up: f() in CyclicSampler

automata.py

@@ -503,16 +503,7 @@ class CyclicSampler(AutomatonSampler):
         + self.__info__
 
   def f(self, x):
-    if OLD_PY_VERSION:
-      # NOTE: for Python 3.7 or below, accumulate doesn't have the 'initial' argument.
-      x_padded = np.concatenate([np.array([0]), x]).astype(np.int64)
-      states = list(itertools.accumulate(x_padded, lambda a,b: (a+b)%self.n ))
-      states = states[1:]
-    else:
-      states = list(itertools.accumulate(x, lambda a,b: (a+b)%self.n, initial=0))
-      states = states[1:] # remove the 1st entry with is the (meaningless) initial value 0
-
-    return np.array(states).astype(np.int64)
+    return np.cumsum(x) % self.n
 
   def sample(self):
     T = self.sample_length()