I tried to get a contour plot of the complex angles of a particular function, but always got one level too many around zeros and infinities. Consider the following MWE which is supposed to plot the contour line forpi / 4 only. It plotspi / 4 alright, but alsopi.

importnumpyasnpimportmatplotlib.pyplotaspltxmin,xmax=-3.0,3.0ymin,ymax=-3.0,3.0nx,ny=500,500x=np.linspace(xmin,xmax,nx)y=np.linspace(ymin,ymax,ny)X,Y=np.meshgrid(x,y)fZ=np.angle(X+1j*Y)plt.contour(X,Y,fZ,levels=[0.25*np.pi],colors="k")plt.gca().set_aspect("equal")plt.show()

This is with mpl 3.4.2.

Edit: A very similar report ison stackoverflow.