以下是一个比较两个范围并在重复时从第三个范围插入值的示例代码：

def merge_ranges(range1, range2, range3):
    merged_range = []

    # 将range1和range2中的元素合并到merged_range中
    for value in range1:
        if value not in merged_range:
            merged_range.append(value)
    for value in range2:
        if value not in merged_range:
            merged_range.append(value)

    # 检查range3中的元素是否与merged_range中的重复
    for value in range3:
        if value not in merged_range:
            merged_range.append(value)

    return merged_range

# 示例用法
range1 = [1, 2, 3, 4]
range2 = [3, 4, 5, 6]
range3 = [4, 5, 6, 7]
merged_range = merge_ranges(range1, range2, range3)
print(merged_range)

运行以上代码将输出：[1, 2, 3, 4, 5, 6, 7]