How to install Python Flask web framework on Debian Wheezy?

Install Flask is very easy and there shouldn't be any troubles with it if you will do the next steps:

1. Install virtual environment for python
This is additional package which is used to provide your future application personal python version.

$ sudo apt-get install python-virtualenv

2. Create your future project directory
Suppose first will be hello_world:
$ mkdir hello_world

3. Create virtual environment for your hello_world project
Suppose virtual environment name will be venv:
$cd ./hello_world
$ virtualenv venv

I had output like that:
New python executable in venv/bin/python
Installing setuptools, pip...done.

4. Activate your environment
$. venv/bin/activate

How your shell prompt should begin from (venv).

5. Create file hello_world.py in current directory with next content:

from flask import Flask
app = Flask(__name__)

@app.route('/')
def hello_world():
    return 'Hello World!'

if __name__ == '__main__':
    app.run()

6. Start application listening on 5000 port

$ python hello_world.py
 * Running on http://127.0.0.1:5000/