reasoning with constraints var_differential[vvar_differential get( , )- elseif varcon not in self conflictswas consisnot now self display( ,"became inconsistent",varconself conflicts add(varconfor in varcon scopev is in one more conflicts var_differential[vvar_differential get( , )+ self variable_pq update_each_priority(var_differentialself display( ,"number of conflicts",len(self conflicts)if not self conflictsno conflictsso solution found self display( ,"solution found:"self current_assignment,"in"self number_of_steps,"steps"return self number_of_steps self display( ,"no solution in",self number_of_steps,"steps"len(self conflicts),"conflicts remain"return none create pq creates an updatable priority queue of the variablesordered by the number of conflicts they participate in the priority queue only includes variables in conflicts and the value of variable is the negative of the number of conflicts the variable is in this ensures that the priority queuewhich picks the minimum valuepicks variable with the most conflicts cspsls py -(continued def create_pq(self)"""create the variable to number-of-conflicts priority queue this is needed to select the variable in the most conflicts the value of variable in the priority queue is the negative of the number of conflicts the variable appears in ""self variable_pq updatable_priority_queue(var_to_number_conflicts {for con in self conflictsfor var in con scopevar_to_number_conflicts[varvar_to_number_conflicts get(var, )+ for var,num in var_to_number_conflicts items()if num> self variable_pq add(var,-numcspsls py -(continued def random_choice(st)"""selects random element from set st it will be more efficient to convert to tuple or list only once ""return random choice(tuple(st)version june