Constraint nodes example (just concept)

gistfile1.txt

# coding: utf-8

# In[34]:


class Node:
    def __init__(self,possibles,value,observers):
        self.possibles = set(possibles)
        self.value = value
        self.observers = set(observers)

    def has_value(self):
        return self.value is not None
    
    def add_observer(self,observer):
        self.observers.add(observer)
        
    def set_value(self,value):
        print("value was set to "+ str(value))
        self.value = value
        self.possibles = set([value])
        self.notify_observers()
 
    def dependency_updated(self,node):
        print("got update")
    
    def notify_observers(self):
        for observer in self.observers:
            observer.dependency_updated(self)
    

class ConstraintEqualNode(Node):
    def __init__(self,lhs,rhs):
        self.lhs = lhs
        self.rhs = rhs 
        self.rhs.add_observer(self)
        self.lhs.add_observer(self)
        self.observers = set()
        self.solved = False
        self.solving = False
        
    def dependency_updated(self,dependency):
        if self.solved or self.solving:
            return
        
        self.solving = True
        if self.lhs.has_value():
            self.rhs.set_value(self.lhs.value)
            self.solved = True
            self.notify_observers()
        
        if self.rhs.has_value():
            self.lhs.set_value(self.rhs.value)
            self.solved = True
            self.notify_observers()
            
        self.solving = False

    

observer_node = Node([3,4],None,[])
test_node = Node([1,2],None,[])
equal_node = ConstraintEqualNode(observer_node,test_node)
test_node.set_value(3)