CentOS and RHEL 7 have Python 2.7 available in the standard packages. You can install Python 3.6 from source while keeping the current 2.7 install on your machine, so any existing dependencies will not break.
yum install gcc yum install zlib-devel yum install openssl-devel yum install sqlite-devel cd /usr/src wget https://www.python.org/ftp/python/3.6.1/Python-3.6.1.tgz tar xzf Python-3.6.1.tgz cd Python-3.6.1 ./configure make altinstall cd .. rm Python-3.6.1.tgz
You can now run python3.6 and pip3.6 from your command line.