The error handling in list_plot is dubious, with the following incredible side effect:

list_plot([(0,-1),(1,-2),(2,-3),(3,-4),(4,None)])

What happens is that list_plot eventually calls point which raises a TypeError due to the None, and then list_plot assumes that it was because the input consists of complex numbers (which is not the reason), and further it assumes that the input data has already been replaced by list(enumerate(data)) by the previous code (which isn't the case), so it takes the second entry of each pair and converts it into an element of CC and plots that. Hence the y-values are plotted on the x-axis. (And the None is converted to 0.)

Component: graphics

Keywords: list_plot, None

Issue created by migration from https://trac.sagemath.org/ticket/29960