help me understand the shell script

help me to understand the below lines in below shell script..

Why we need to use virtualenv "$ANSIBLE_ROOT" .... and what is the use of virtualenv here ....

and how activate and deactivate worked ...i am bit confused how activate and deactivate keywords worked here..
. "$ANSIBLE_ROOT/bin/activate"
deactivate

and also how pip works with -i option...i.e. below

pip install docker-compose==1.15.0 -i https://artifactory.global.raju.com/artifactory/api/pypi/pypi-release/simple

#!/usr/bin/env sh

ANSIBLE_ROOT=${ANSIBLE_ROOT:-~/ansible}
scl enable python27 bash <<!
set -e
export https_proxy=https://10.198.140.122:8080
if [ ! -d "$ANSIBLE_ROOT/bin" ]
then
    virtualenv "$ANSIBLE_ROOT"
    . "$ANSIBLE_ROOT/bin/activate"
    echo "Installing latest version of ansible"
    pip install ansible -i https://artifactory.global.raju.com/artif4actory/api/pypi/pypi-release/simple
    pip install docker-py -i https://artifactory.global.raju.com/artifactory/api/pypi/pypi-release/simple
    pip install docker-compose==1.15.0 -i https://artifactory.global.raju.com/artifactory/api/pypi/pypi-release/simple
    deactivate
fi
!

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