update python debian

# check python version
python3 --version  #output: Python 3.7.3

# Open the /etc/apt/sources.list file with the following command:
sudo nano /etc/apt/sources.list
 
# Add the official testing repository. Append the following line of text to 
# the end of the file:
deb http://http.us.debian.org/debian/ testing non-free contrib main
  
# After editing the file, download the information for all of the packages 
# available with the following command:
sudo apt update

#Upgrade Python 3 with the following command:
sudo apt upgrade python3

#Verify that you’ve updated Python by checking the version:
python3 --version #output: Python 3.9.1