Differences between class_weight and scale_pos weight in LightGBM
You can achieve the same results by using either class_weight, scale_pos_weight and is_unbalanced for binary classification on unbalanced dataset.
Setting
class_weight = {0: (number of negative samples / number of positive samples), 
                1: (number of positive samples / number of negative samples)}

is the same as setting is_unbalance = True or scale_pos_weight = (no. of negative samples / number of positive samples).