1. Switch the default Python version
Use the following command to view the version number information that can be replaced:
update-alternatives --list python
If an error message appears after executing the command
update-alternatives: error: no alternatives for python
Indicates that the alternative version of Python has not been installed, execute the following command to install it:
sudo update-alternatives --install /usr/bin/python python /usr/bin/python2.7 1
sudo update-alternatives --install /usr/bin/python python /usr/bin/python3.5 2
After execution, you will find that the default Python version of the system is Python3.5. Re-execute
update-alternatives --list python, and the output is as follows:
At this time, we can switch the Python version:
sudo update-alternatives --config python
The output is as follows:
Enter the corresponding serial number to select the default version.
2. Problems encountered when executing pip
Install pip:
sudo apt-get install python-pip(Python2安装)
sudo apt-get install python3-pip(Python3安装)
Check the pip version number:
pip --version
1. The following problems may occur:
Traceback (most recent call last): File “/usr/local/bin/pip”, line7, in module
from pip._internal import main
ImportError: No module named _internal
Forcibly reinstall pip to solve the problem:
wget https://bootstrap.pypa.io/get-pip.py --no-check-certificate
sudo python get-pip.py --force-reinstall(重装Python2)
sudo python3 get-pip.py --force-reinstall(重装Python3)
2. There is a problem after upgrading pip
Upgrade the pip version:
sudo pip install --upgrade pip
If you encounter an error during use after upgrading:
ImportError: cannot import name main
Solution:
sudo gedit /usr/bin/pip
Will
from pip import main
if __name__ == '__main__':
sys.exit(main())
changed to
from pip import __main__
if __name__ == '__main__':
sys.exit(__main__._main())