diskimage-builder/elements/pip-and-virtualenv/install.d/pip-and-virtualenv-source-install/04-install-pip

#!/bin/bash

if [ ${DIB_DEBUG_TRACE:-0} -gt 0 ]; then
    set -x
fi
set -eu
set -o pipefail

if [[ $DISTRO_NAME =~ (centos|fedora) ]]; then
    # GENERAL WARNING : mixing packaged python libraries with
    # pip-installed versions always creates issues.  Upstream
    # openstack-infra uses this a lot (especially devstack) but be
    # warned: here be dragons :)

    # Firstly we want to install the system packages.  Otherwise later
    # on somebody does a "yum install python-virtualenv" and goes and
    # overwrites the pip installed version with the packaged version,
    # leading to all sorts of weird version issues.
    ${YUM:-yum} install -y python-virtualenv python-pip python-setuptools

    # install pip; this overwrites packaged pip
    /usr/local/bin/dib-python /tmp/get-pip.py

    # pip and setuptools are closely related; we want to ensure the
    # latest for sanity.  Because distro packages don't include enough
    # info in the egg for pip to be certain it has fully uninstalled
    # the old package, for safety we clear it out by hand (this seems
    # to have been a problem with very old to new updates,
    # e.g. centos6 to current-era, but less so for smaller jumps).
    # There is a bit of chicken-and-egg problem with pip in that it
    # requires setuptools for some operations, such as wheel creation.
    # But just installing setuptools shouldn't require setuptools
    # itself, so we are safe for this small section.
    rm -rf /usr/lib/python2.7/site-packages/setuptools*
    pip install -U setuptools

    # now install latest virtualenv.  it vendors stuff it needs so
    # doesn't have issues with other system packages.
    pip install -U virtualenv

    # Add this to exclude so that we don't install a later package
    # over it if it updates.  Note that fedora-minimal, bootstrapped
    # via yum, can have an old yum.conf around, so look for dnf first.
    if [[ -f /etc/dnf/dnf.conf ]]; then
        conf=/etc/dnf/dnf.conf
    elif [[ -f /etc/yum.conf ]]; then
        conf=/etc/yum.conf
    else
        die "No conf to modify?"
    fi
    echo "exclude=python-virtualenv,python-pip,python-setuptools" >> ${conf}
else
    /usr/local/bin/dib-python /tmp/get-pip.py
    pip install virtualenv
fi