<span class="n">get_kline_serial</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">symbol</span><span class="p">,</span> <span class="n">duration_seconds</span><span class="o">=</span><span class="mi">60</span><span class="p">,</span> <span class="n">data_length</span><span class="o">=</span><span class="n">data_length</span><span class="p">) 这个函数，为什么 这里是3个参数，有一些是2个参数(没有那个data_length)，有啥区别？</span>
