Package Acquisition

Retrieve the package managers for both Python versions using the system repository:

sudo apt-get update
sudo apt-get install python-pip python3-pip

Locating Interpreter Binaries

Determine the exact filesystem paths for the installed interpreters:

command -v python2.7
command -v python3.6

Typically, these resolve to /usr/bin/python2.7 and /usr/bin/python3.6.

Establishing Shell Aliases

Open the shell configuration file for editing:

nano ~/.bashrc

Append alias definitions at the end of the file to enforce explicit interpreter and package manager paths:

alias pip2='/usr/bin/pip2'
alias pip3='/usr/bin/pip3'
alias python='/usr/bin/python2.7'
alias python3='/usr/bin/python3.6'

Apply the modifications immediately:

source ~/.bashrc

Adjusting Executable Entry Points

System updates may overwrite pip executables. Modifying the entry point scripts ensures correct interpreter invocation and compatibility.

Configuring /usr/bin/pip2

Edit the Python 2 package manager script:

sudo nano /usr/bin/pip2

Replace its contents with a streamlined entry point pointing to Python 2.7:

#!/usr/bin/python2.7
# Dynamic entry point for Python 2 package management
import sys
from pip import main as run_pip2

if __name__ == '__main__':
    sys.exit(run_pip2())

Configuring /usr/bin/pip3

Edit the Python 3 package manager script:

sudo nano /usr/bin/pip3

Implement logic to handle the API transition in newer Python 3 versions and prevent execution under incorrect interpreters:

#!/usr/bin/python3
# Dynamic entry point for Python 3 package management
import sys

current_major = sys.version_info[0]
current_minor = sys.version_info[1]

def execute_pip():
    if current_major != 3:
        print(f"Error: Python {current_major} detected. pip3 requires Python 3.")
        print("Switch versions using 'update-alternatives --config python'.")
        return 1
    
    # Handle API changes for Python 3.8+
    if current_minor >= 8:
        from pip import __main__
        return __main__._main()
    
    from pip import main
    return main()

if __name__ == '__main__':
    sys.exit(execute_pip())

Validation

Confirm that the binaries resolve to the expected versions:

python --version
pip2 --version
python3 --version
pip3 --version