Problem statement
With the sudden rise of python3, the Kali 2020 version has removed pip2. Since many previous hacking tools were written by python2, the corresponding modules need to be installed through pip2.
Solution
Step 1: Download get-pip.py
wget https://bootstrap.pypa.io/pip/2.7/get-pip.py 
Step 2: execute get-pip.py in python
sudo python2 get-pip.py
Step 3: Verify the environment
pip2 -V
Step 4: Use pip2 to install third-party libraries and packages
