If you have pip installed within python you can install many packages easily. Flask is one of the packages available.
To install flask using pip the below can be executed.
root@computer:/# pip install flask
Collecting flask
Downloading Flask-0.12.2-py2.py3-none-any.whl (83kB)
100% |████████████████████████████████| 92kB 2.0MB/s
Collecting click>=2.0 (from flask)
Downloading click-6.7-py2.py3-none-any.whl (71kB)
100% |████████████████████████████████| 71kB 8.0MB/s
Collecting Werkzeug>=0.7 (from flask)
Downloading Werkzeug-0.12.2-py2.py3-none-any.whl (312kB)
100% |████████████████████████████████| 317kB 3.3MB/s
Collecting Jinja2>=2.4 (from flask)
Downloading Jinja2-2.9.6-py2.py3-none-any.whl (340kB)
100% |████████████████████████████████| 348kB 3.0MB/s
Collecting itsdangerous>=0.21 (from flask)
Downloading itsdangerous-0.24.tar.gz (46kB)
100% |████████████████████████████████| 51kB 2.8MB/s
Collecting MarkupSafe>=0.23 (from Jinja2>=2.4->flask)
Downloading MarkupSafe-1.0.tar.gz
Building wheels for collected packages: itsdangerous, MarkupSafe
Running setup.py bdist_wheel for itsdangerous … done
Stored in directory: /root/.cache/pip/wheels/fc/a8/66/24d655233c757e178d45dea2de22a04c6d92766abfb741129a
Running setup.py bdist_wheel for MarkupSafe … done
Stored in directory: /root/.cache/pip/wheels/88/a7/30/e39a54a87bcbe25308fa3ca64e8ddc75d9b3e5afa21ee32d57
Successfully built itsdangerous MarkupSafe
Installing collected packages: click, Werkzeug, MarkupSafe, Jinja2, itsdangerous, flask
Successfully installed Jinja2-2.9.6 MarkupSafe-1.0 Werkzeug-0.12.2 click-6.7 flask-0.12.2 itsdangerous-0.24