PYTHA allows you to show only parts that you want to on your Parts List. If you wish to include or exclude all parts within a specific Layer from a Parts List select Layer under Filter in the Parts List menu. This will open the Layer selection dialogue - all Layers currently selected to appear on your Parts List will be ticked. Simply select or deselect the Layers you wish to add or remove then confirm. Your Parts List will be updated to contain your new Layer selection. 

NOTE: If some of the parts that you have selected are not appearing on your Parts List, you should check your Layer selection to ensure that none are deselected that shouldn't be.