 defined executor must be an instance of a </span><span class="se">\</span>
<span class="s2">        child class of the Executor class defined in pyquokka.executors. You must override the execute and done methods.&quot;</span>

    <span class="n">select_stream</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">select</span><span class="p">(</span><span class="n">required_columns</span><span class="p">)</span>

    <span class="n">custom_node</span> <span cla