[python] Set markers for individual points on a line in Matplotlib

Hello There is an example:

import numpy as np
import matplotlib.pyplot as ptl

def grafica_seno_coseno():
    x = np.arange(-4,2*np.pi, 0.3)
    y = 2*np.sin(x)
    y2 = 3*np.cos(x)
    ptl.plot(x, y,  '-gD')
    ptl.plot(x, y2, '-rD')
    for xitem,yitem in np.nditer([x,y]):
        etiqueta = "{:.1f}".format(xitem)
        ptl.annotate(etiqueta, (xitem,yitem), textcoords="offset points",xytext=(0,10),ha="center")
    for xitem,y2item in np.nditer([x,y2]):
        etiqueta2 = "{:.1f}".format(xitem)
        ptl.annotate(etiqueta2, (xitem,y2item), textcoords="offset points",xytext=(0,10),ha="center")
    ptl.grid(True)
    return ptl.show()