As there are a lot of software in Raspbian. I delete the software below:
sudo apt-get purge wolfram-engine
sudo apt-get purge sonic-pi
sudo apt-get purge scratch
sudo apt-get purge python
sudo apt-get purge python3
sudo apt-get purge python-pygame
sudo apt-get purge bluej
sudo apt-get purge scratch
sudo apt-get purge nuscratch
sudo apt-get purge greenfoot
sudo apt-get autoremove
After reboot, I could not log in to PIXEL anymore. I have input the right password, but it does not work. I do not know why. What should I do to log in to PIXEL again.