Code tweak to '== None'

darius · darius · commit ecc6b7551986 · 2011-10-23T10:06:15.000Z
diff --git a/csp.py b/csp.py
@@ -70,8 +70,8 @@ def nconflicts(self, var, val, assignment):
         "Return the number of conflicts var=val has with other variables."
         # Subclasses may implement this more efficiently
         def conflict(var2):
-            val2 = assignment.get(var2, None)
-            return val2 != None and not self.constraints(var, val, var2, val2)
+            return (var2 in assignment
+                    and not self.constraints(var, val, var2, assignment[var2]))
         return count_if(conflict, self.neighbors[var])
 
     def display(self, assignment):
diff --git a/mdp.py b/mdp.py
@@ -59,7 +59,7 @@ def __init__(self, grid, terminals, init=(0, 0), gamma=.9):
                     self.states.add((x, y))
 
     def T(self, state, action):
-        if action == None:
+        if action is None:
             return [(0.0, state)]
         else:
             return [(0.8, self.go(state, action)),
diff --git a/search.py b/search.py
@@ -193,7 +193,7 @@ def recursive_dls(node, problem, limit):
                 result = recursive_dls(successor, problem, limit)
                 if result == 'cutoff':
                     cutoff_occurred = True
-                elif result != None:
+                elif result is not None:
                     return result
             return if_(cutoff_occurred, 'cutoff', None)
 
diff --git a/utils.py b/utils.py
@@ -481,7 +481,7 @@ def mean(values):
 def stddev(values, meanval=None):
     """The standard deviation of a set of values.
     Pass in the mean if you already know it."""
-    if meanval == None: meanval = mean(values)
+    if meanval is None: meanval = mean(values)
     return math.sqrt(sum([(x - meanval)**2 for x in values]) / (len(values)-1))
 
 def dotproduct(X, Y):
