demo_python/d_op.py - 3//2 == 1 , 4//2 == 2 , 5//2 == 2
demo_python/d_plot.py matplotlib.plot figure, add text , savefig
demo_python/p_plot/d_pylab.py show img, write text , ratio
demo_python/d_str.py ascii_to_char
demo_curwork/Gotex-understand,run