human
Solve the following python programming problem given the following code:
def register(self, a, b, cost = 1.0) : 
    sigs = expand_tuples ([a, _]) 
    def _(func) : 
        for (a, b) in sigs : 
            self.graph.add_edge (b, a, cost = cost, func = func) 
return func 
return _ 

    
    

    Fix the buggy line: sigs = expand_tuples ([a, _])
assistant
#Here is Python code to fix the buggy line: sigs = expand_tuples ([a, _])
.

sigs = expand_tuples ([a, b])