diskimage-builder/diskimage_builder/elements/pip-and-virtualenv

pip-and-virtualenv

This element installs pip and virtualenv in the image.

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).

Namespacing of the tools will be up to your distribution. Some 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). Other platforms have avoided making a decision and require explicit version suffixes.

To install pip and virtualenv from package:

export DIB_INSTALLTYPE_pip_and_virtualenv=package

Source install

Note

For source installs this element setups and Python 2 and Python 3 environments. This means it will bring in python2 packages, so isn't appropriate if you want a python3 only environment.

Note

Source install is considered deprecated for several reasons. Because it makes for a hetrogenous environment between distro packaged tools and upstream it means the final images create bespoke environments that make standarised testing difficult. The tricks used around holding packages to overwrite them cause difficulty for users of images. This also brings in Python 2 unconditonally, something not wanted on modern Python 3 only distributions.

Source install is the default on most platforms for historical purposes. The current exception(s) are RHEL8 and CentOS 8.

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

Source installs from upstream releases are not name-spaced. It is inconsistent across platforms if the first or last install will 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.

Environment Variables

To simplify the common-case of "install a package" or "create a virtualenv" with the default system Python, the following variables are exported by this element:

• DIB_PYTHON_PIP
• DIB_PYTHON_VIRTUALENV

This will create/install using the dib-python version for the platform (i.e. python2 for older distros, python3 for modern distros). Note that on Python 3 platforms it will use the inbuilt venv (rather than the virtualenv package -- if you absolutely need features only virtualenv provides you should call it directly in your element; see below).

Explicit use of 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.