pip-and-virtualenv

This element installs pip and virtualenv in the image.

Note

This element setups and Python 2 and Python 3 environment. This means it will bring in python2 packages, so isn’t appropriate if you want a python3 only environment.

Package install

If the package installtype is used then these programs are installed from distribution packages. In this case, pip and virtualenv will be installed only for the python version identified by dib-python (i.e. the default python for the platform).

Distribution packages have worked out name-spacing such that only python2 or python3 owns common scripts like /usr/bin/pip (on most platforms, pip refers to python2 pip, and pip3 refers to python3 pip, although some may choose the reverse).

To install pip and virtualenv from package:

export DIB_INSTALLTYPE_pip_and_virtualenv=package

Source install

Source install is the default. If the source installtype is used, pip and virtualenv are installed from the latest upstream releases.

Source installs from these tools are not name-spaced. It is inconsistent across platforms if the first or last install gets to own common scripts like /usr/bin/pip and virtualenv.

To avoid inconsistency, we firstly install the packaged python 2 and 3 versions of pip and virtualenv. This prevents a later install of these distribution packages conflicting with the source install. We then overwrite pip and virtualenv via get-pip.py and pip respectively.

The system will be left in the following state:

  • /usr/bin/pip : python2 pip

  • /usr/bin/pip2 : python2 pip (same as prior)

  • /usr/bin/pip3 : python3 pip

  • /usr/bin/virtualenv : python2 virtualenv

(note python3 virtualenv script is not installed, see below)

Source install is supported on limited platforms. See the code, but this includes Ubuntu and RedHat platforms.

Using the tools

Due to the essentially unsolvable problem of “who owns the script”, it is recommended to not call pip or virtualenv directly. You can directly call them with the -m argument to the python interpreter you wish to install with.

For example, to create a python3 environment do:

# python3 -m virtualenv myenv
# myenv/bin/pip install mytool

To install a python2 tool from pip:

# python2 -m pip install mytool

In this way, you can always know which interpreter is being used (and affected by) the call.

Ordering

Any element that uses these commands must be designated as 05-* or higher to ensure that they are first installed.