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deal with failures

Let’s fix the code

def dfs(variables, constraint):
    # manage filtering failure

>>🥛<<

Let’s fix the code

def dfs(variables, constraint):
    if constraint.filter(variables) is False:
        return 0
    var, val = make_decision(variables)
    if var is None:
        print(variables)
        return 1
    else:
        n = propagate(variables, var, val, True, constraint)
        n += propagate(variables, var, val, False, constraint)
        return n

None and True will be used later.

This code

variables = {"x1": {3, 4},
             "x2": {2, 3}}
c1 = LessThan("x1", "x2")

print("There are", dfs(variables, c1), "solutions")

outputs:

There are 0 solutions