Gurobi Python constraint adding

I want to write the following constraint in gurobi python ,

and I am writing that as the following and having key error. Can anyone help me by saying where I am doing mistake?

for (i,j) in road_node:
    for t in range(1,n_time_horizon+1):
        m.addConstr(sum([x[v,i,u,j,u+fftt[(i,j)]] for v in vehicle_list for u in range(1,n_time_horizon+1) if u>=0 and u<=t]) - sum([x[v,j,u,i,u+fftt[(j,i)]] for v in vehicle_list for (j,i) in road_node for u in range(1,n_time_horizon+1) if u>=0 and u<=t]) <= l[(i,j)],name = "cont_4")

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