Fix compatibility with matplotlib 3.8.0
This PR updates the handling of the PlotArgsProcessor
class that overrides the builtin _process_plot_var_args
private object that does all of the low-level argument handling and line generation for Axes.plot()
.
In matplotlib <3.8.0 the parent Axes
object is passed to the constructor, while in >=3.8.0 that is passed to the caller.