I think it might be useful to have a fastplotlib submodule with all the base classes that are used throughout the library. This would include:

• Graphic
• PlotArea
• Subplot
• Figure
• Legend
• UI base classes

The reason this could be useful is to have a central location of all bases so that they can be used everywhere for type annotations without circular imports.

I think this is a reasonable idea for a library like ours. For example, in pyqtgraph you can do GraphicsItem.getViewBox() which returns a ViewBox (but there is no type annotation). And ViewBox itself inherits from GraphicsItem. We don't have circumstances like this, but it would be useful to type annotate Subplot.parent is Figure, and simultaneously that Figure contains Subplots.