Difference between revisions of "Python-Flask/C2/Installation-of-Python-Flask/English"

• Create a Virtual Environment.
• Activate and deactivate the Virtual Environment.
• Install packages inside the Virtual Environment.
• And launch a Flask application.

• Ubuntu Linux 16.04 OS
• Python 3.5.2
• Atom text editor 1.22.1
• Firefox web browser and
• A working Internet connection.

You can use any text editor and web browser of your choice.

Pre-requisites

• Linux commands and

• Basic Python programming

If not, then please go through the corresponding tutorials on this website.

• A virtual environment is a self-contained directory tree.
• It contains a Python installation for a particular version of Python.
• Additional packages can be installed inside the virtual environment.

• Venv is the short form for virtual environment.
• Venv is used to avoid conflict between different Python installations.

• For every project, we can have a separate Venv.
• We will install Venv via a package called pip.

• Pip is a package manager program.
• Used to install, upgrade, and remove Python packages.
• Pip3 is the Python3 version of pip

• To check if pip3 is already installed, type the following command in the terminal:

pip3 <space> hyphen hyphen version and press Enter.

• If it gives a version number, then you don’t need to install it again.
• Else, install pip3 using the following command in the terminal:

sudo <space> apt <space> install <space> python3-pip

Type pip3 <space> hyphen hyphen version and press Enter.

Point to pip version

In my case it is pip 18.0 for python 3.5.

$ sudo pip3 install virtualenv [Enter]

And press Enter.Provide the admin password and press Enter.

This folder will help me to organize my files in a single place.

Type mkdir project_flask [Enter]

Type cd project_flask [Enter]

Typing

$ virtualenv -p python3 flask_venv

virtualenv <space> <hyphen> p <space> python3 <space> flask_venv

This will create a virtual environment named flask_venv.

You may choose any other name for the virtual environment.

The hyphen p flag is used to specify which python interpreter is to be used.

Typing

$ virtualenv -h [Enter]

virtualenv -h and press Enter.

Here, we can see the list of available commands and options.

Type $ ls [Enter]

Note that we have a folder named flask_venv in our current directory.

Type

$ ls flask_venv [Enter]

Type ls <space> flask underscore venv

Press Enter.

Point to the list of directories in the terminal

site-packages.

lib/ python3.5 directory

Activate means, from now on all the python commands will run inside this venv.

Typing

$ . flask_venv/bin/activate

Type dot <space> flask <underscore> venv slash bin slash activate

Press Enter.

Highlight

(flask_env)

We can see the name of the virtual environment flask_venv inside parentheses, in the terminal.

This indicates that we are inside an activated virtual environment called flask_venv.

Type

$ python3 -V

For that, type python3 <space> hyphen capital V and press Enter.

In my case it shows Python 3.5.2.

Typing

$ pip3 install flask

Type pip3<space> install <space> flask and press Enter.

This will install the Flask package only for this venv and not system wide.

Highlight

“...installed Flask-1.0.2 Jinja2-2.10 MarkupSafe-1.0 Werkzeug-0.14.1...”

Type

$pip list

pip <space> list

And press Enter.

Highlight flask, jinja2, werkzeug.

That means our Flask installation was successful.

This is so that the flask_venv is logically separated from the hello world app.

However, you can use any text editor of your choice.

$ atom hello_flask.py

atom <space> hello underscore flask dot py

and press Enter.

from flask import Flask

app = Flask(__name__)

@app.route('/')

def hello_world():

(Tab)return 'Hello, World!'

Which will launch a very simple built-in server.

Type

$ export FLASK_APP=hello_flask.py

export <space> FLASK_APP <equal to> hello underscore flask dot py

And press Enter.

The FLASK_APP variable specifies the module to import while running our app.

This tells the terminal which flask app to work with.

Type

$ echo $FLASK_APP

To do that type

echo <space> <dollar> FLASK underscore APP

And press Enter.

Type

$ python3 -m flask run

[Enter]

python3 <space> hyphen m <space> flask <space> run

This command runs the flask application named hello underscore flask.

The file to execute is the one given by the FLASK_APP environment variable.

We have already set that in the previous step.

Press Enter.

“Running on http://127.0.0.1:5000/”

This implies that the server is running locally.

Type

http://127.0.0.1:5000/

And press Enter.

In the address bar, type http://127.0.0.1:5000/ and press Enter.

Which means that Flask is working fine in the Virtual Environment.

Type deactivate and press Enter

To do so, type deactivate and press Enter.

Point the shell prompt

Let us summarize.

• Activate and deactivate the Virtual Environment.
• Install Flask and
• Launch “Hello world” in Flask.

Please download and watch it.

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