install pip for python2 and 3

install_pip.md

For operation systems: Ubuntu, Debian, and MacOS. In windows the pip and virtualenv commands should be the same once python is installed somewhere.

Install pip, virtualenv, and python module in virtualenv

Debian/Ubuntu

Use python module psutil as example.

> sudo apt update
> sudo apt install python-pip virtualenv
> /usr/bin/virtualenv ~/venv  # create virtualenv in ~/venv
> source ~/venv/bin/activate  # enter venv
(venv) > pip install psutil  # install python module in venv

Need to enter venv (source ~/venv/bin/activate) in order to run python scripts which use the module psutil. If don't want to manually activate there are two ways:

1. Add the following line to ~/.bashrc (bash) or ~/.zshrc (zsh)
   • source ~/venv/bin/activate
2. Install psutil globally (for the user) without using virtualenv:
   • > /user/bin/pip install psutil --user

Personally I prefer NOT to install globally for the user (exceptions: pylint/pyflakes). Sometimes, for some reason, there are multiple python in $PATH and it's confusing which python/pip and $PYTHONPATH is using (in my mac for example, I mainly use python2/3 from miniconda, but there are also python from macports due to dependencies and python from MacOS).

Mac

In mac, install pip via get-pip.py or anaconda/miniconda or macports or homebrew or the python installer from python.org (pip included). Apart from get-pip.py, all other methods also install a python binary somewhere.

Then install virtualenv via pip (or use conda/port/brew if install python and pip via these package managers).

For example (in mac, use get-pip.py, install pip, virtualenv, create virtualenv venv, and in venv install python module psutil):

> curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py
> /usr/bin/python get-pip.py --user  # make sure using the python2.7 in MacOS
# now pip is in ~/Library/Python/2.7/bin
> ~/Library/Python/2.7/bin/pip install virtualenv --user
> ~/Library/Python/2.7/bin/virtualenv ~/venv
> source ~/venv/bin/activate
(venv) > pip install psutil  # install psutil in venv; note that pip is also from the virtualenv

One can add ~/Library/Python/2.7/bin into $PATH. I prefer not to do so. Once enter venv there are already python and pip in $PATH, so unless you need to install python modules globally (for the user) or using the virtualenv command frequently, there's probably no need to update $PATH.

Also see above Debian/Ubuntu section in how to enter venv automatically or install the module globally for the user so that there's no need to source ~/venv/bin/activate every time.

usage of virtualenv

• enter venv: ~/venv/bin/activate
• leave venv: deactivate

remove the venv: rm -rf ~/venv

python3 virtualenv

To create a python3 virtualenv in Ubuntu/Debian:

> sudo apt install python3-pip
> /usr/bin/python3 -mvenv ~/py36env
> source ~/py36venv/bin/activate

In mac if there's already a python3 somewhere (here use python3 installed by macports as example):

> /opt/local/bin/python3.7 -mvenv ~/venv37
> source ~/venv37/bin/activate

note about anaconda/miniconda

anaconda/miniconda are probably more for scientific computing in python. minoconda is the lighter version of anaconda. They come with a package manager conda. They have their own commands to manage environments, please refer to their documents. After create virtual environments, one can use their conda and/or pip to install python modules.