epubjs-reader VS PyQtGraph

There's a few JS libraries that allows you to basically have the same functionality, example: https://github.com/futurepress/epubjs-reader/

PyQtGraph - Interactive and realtime 2D/3D/Image plotting and science/engineering widgets.

Image, 3D, or data visualization applications using OpenCV and the SciPy ecosystem. The Graphics View Framework can display an image and let the user interact with it, and the Python ecosystem is very rich for image processing, data analysis, and visualization. For example, LabelMe for image labeling, PyQtGraph for scientific graphics, or custom QWidget integration in Maya.

I don't think that's related to your error though - from the backtrace, it looks like the plotWidget has plotItem attribute that's somehow been assiged to itself (or maybe some other PlotWidget) , so is just endlessly recursing as it tries to proxy the same attribute lookup (presumably 'clear') to itself. Looking at the source, the plotitem is either created as a new PlotItem() object if not provided, or passed in to the constructor, so I'd check how this gets initialised - eg. does this get set as a property in your .ui file? Are you setting it to the widget itself somehow?

I did something like this recently but I used pyqtgraph: https://www.pyqtgraph.org/

Ah, I agree, Matplotlib is for publication, so slow and pretty. For fast, I use pyqtgraph, which can do that 10 million point plot interaction. And since it's QT, it integrates seamlessly into QT applications.