How to uninstall Python 2.7 (installed by yourself) on a Mac OS

1. Open the terminal.

2. Remove the Python 2.7 framework:
    sudo rm -rf /Library/Frameworks/Python.framework/Versions/2.7

3. Remove the Python 2.7 applications directory: 
    sudo rm -rf "/Applications/Python 2.7"
    
4. Remove the symbolic links in /usr/local/bin that point to Python 2.7:
    cd /usr/local/bin
    ls -l . | grep '../Library/Frameworks/Python.framework/Versions/2.7' | awk   '{print $9}' | xargs sudo rm

5. Back to the system default Python:
    cd /Library/Frameworks/Python.framework/Versions
    sudo rm Current
    sudo ln -s /usr/bin/python Current

PS: If you do not carry out Step 5, then there will be an error when you start python in the terminal.