Introduction To Python Flask - Beginners Guide
Python Flask Tutorial Introduction Flask
This introductory Python Flask
tutorial explains what is Flask, Python installation, Virtualenv, Flask Hello
World example with a section on code examples, debugging and testing:
Web development is a greater amount of a craftsmanship than an expertise. It requires persistence and determination as well as diligence, mental fortitude and commitment to make what is important to find success. These days, understudies ought to advance as fast as could be expected.
We made this Python Flask instructional exercise for understudies to accelerate and carry out straightforward and complex web programming utilizing Python 3.
This Python Flask instructional exercise is more similar to the cup amateur instructional exercise which covers introducing Python, Virtualenv, and other vital bundles. In this instructional exercise series, we will likewise introduce Flask alongside other fundamental Flask modules. We likewise remembered a segment for code investigating, testing, and constant coordination utilizing Git activities.
You May Also Like : Linux Tip - How to Create and Manage Virtual Python Environments
What is Flask
Flask is a web development
framework. It is a framework with a built-in development server and debugger.
The
very structure of Flask differs from other archetypes in that it allows web
developers the flexibility and convenience to adapt to frequently made changes
in the developer community.
What
is the stock for
We
use the Flask framework to create web applications in the Python programming
language. Integrates with other third-party services and APIs to ensure
the richness and relevance of your application under development. The
basic concepts of Flask are simple and space-saving.
Let's start with this Python Flask tutorial to understand web development with the Flask GitHub repository. However, before continuing, clone your project from Github to make it easier to follow up on the code examples discussed.
Prerequisites
In
addition to the headings mentioned in this section, we recommend that you
create a Github account. Let's move on to the steps below in the
prerequisites.
Step 1: Install Python
Check
if you have Python 3 installed or not. If not, download Python 3 from here and install it according to your operating system.
Step 2: Create a Python virtual
environment
python3 -m venv venv
Use the command below to activate the Python virtual environment.
source venv/bin/activate
Below is an example of
activating and deactivating a virtual environment.
All
subsequent commands in this tutorial should run in an activated virtual
environment. Install the wheel pack so that we can build wheels in a
virtual environment.
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pip install wheel
Step 3: Download and Install Flask
We
need to follow the Flask download steps and install Flask by following the
steps below.
Now
install Flask.
pip install flask
Some of us like to work with
the latest changes to the source code. We can use the command below to
install with the latest changes to Flask sources.
Create
a temporary directory.
mkdir tmp
Now install Flask from the
Github repository. You must remain connected to the internet for the
command below to work.
Look at the console outputs to
check for successful installation. Now check if we have access to Flask
commands.
flask --help
You can see some exceptions
regarding the lack of the Flask app. However, neglect them, as we haven't
created any Flask app. Our app is an instance of Flask, which is a wrapper
in the Werkzeug framework and Jinja template engine.
Tool
Werkzeug
is a WSGI toolkit. WSGI is just a convention for web servers forwarding
web requests to web
applications written in the Python programming language.
Jinja
Step 4: Install MongoDB
Follow the means beneath to introduce MongoDB. We have framed the moves toward introduce it on a Debian based Linux framework. In the event that you are utilizing an alternate operating system access associate and introduce as per your expected operating system.
Install gnupg to import MongoDB
public GPG key.
sudo apt-get install gnupg
Now import the key with the command below.
Create a source list file according to your Linux distribution. We
have added a list of sources according to Debian.
echo 'deb http://repo.mongodb.org/apt/debian
buster/mongodb-org/4.2 main' | sudo tee
/etc/apt/sources.list.d/mongodb-org-4.2.list
Run the update command
sudo apt-get update
Now install MongoDB using the command below.
sudo apt-get install -y mongodb-org
After the installation is successful, run MongoDB with the command
below.
sudo systemctl start mongod
Check the status of MongoDB with the command below.
Now make sure mongod automatically restarts on system reboot by
issuing the command below.
sudo systemctl enable mongod
Now check if you can connect to the MongoDB server using the mongo
client.
mongo
In a mongo shell, try to use
help and display the dbs commands.
Create a Flask app
Use the command below to
install flask-appbuilder and mongoengine.
pip install flask-appbuilder pip install
mongoengine pip install flask_mongoengine
Create a scaffolded app with values displayed as comments in the
following code snippet.
We will see an output similar
to the one given below.
Your new app name: exampleApp Your engine type,
SQLAlchemy or MongoEngine (SQLAlchemy, MongoEngine) [SQLAlchemy]: MongoEngine
Downloaded the skeleton app, good coding!
Take a look at the layout of the project and application. Below
we have shown the output of the tree command.
# Theme configuration for Cybord=g # these
themes are located on static/appbuilder/css/themes # We can create our own and
easily use them by placing them on the same dir structure to override
#APP_THEME = 'bootstrap-theme.css' # default bootstrap #APP_THEME =
'cerulean.css' # cerulean #APP_THEME = 'amelia.css' # amelia theme #APP_THEME =
'cosmo.css' # cosmo theme APP_THEME = 'cyborg.css' # cyborg theme #APP_THEME =
'flatly.css' # flatly theme
To run a scaffolded application,
use the command below in a terminal.
flask run
Flask
Hello World
To
create the first program in flaskTutorialApp, open the views.py file
in the application directory and add the following code. Look for the
import instructions provided in the file. Add these statements if they
don't already exist.
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from flask_appbuilder import BaseView, expose
from app import appbuilder class HelloWorld(BaseView): ''' This first view of
the tutorial ''' route_base = '/hello' @expose('/') def hello(self): return
'Hello, World! from Software Testing Help' # at the end of the file
appbuilder.add_view_no_menu(HelloWorld())
Save the file after adding the
above source code. Go to the project root directory and use the command
below to start the Flask development server.
flask run
Now go to http: // localhost:
5000 / hello / to see the output in the browser.
Dbms Open Source Is:
Debugging
Currently
the development server is not in debug mode. Without debug mode, it's hard
to find bugs in your Flask application's source code.
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The debugging mode in Flask
produces the following results:
1. Troubleshoot mode actuates programmed reloading. This intends that subsequent to making changes to the application source code, we don't need to restart the advancement server.
2. Troubleshoot mode actuates the Python debugger. We can really look at the upsides of the factors during the special case.
3. Troubleshoot mode permits you to investigate your Flask application. We can really look at the upsides of different factors during an investigating meeting.
Stop the advancement server on the off chance that it's now running. You can utilize CTRL + C or Keyboard Break to do likewise.
Use the code below to enable
debug mode and temporarily start the development server.
FLASK_ENV=development flask run
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Look
for the debugger PIN in the console and make a note of it.
Now
let's change the above HelloWorld view with the following lines of the code
snippet. Note that we made a custom exception.
@expose('/') def hello(self): raise
Exception('A custom exception to learn DEBUG Mode') return 'Hello, World! from
Software Testing Help'
Likewise, investigate the control center the advancement server is running on. You will figure out that this opportunity changes to the views.py document are recognized naturally and the investigate server begins without anyone else. Presently we don't have to restart it physically.
The console will have lines as
shown below. We need to note the debug PIN for later.
* Detected change in 'https://cdn.softwaretestinghelp.com/work/sth/flaskTutorialApp/app/views.py', reloading 2020-06-02 14:59:49,354:INFO:werkzeug: * Detected change in 'https://cdn.softwaretestinghelp.com/work/sth/flaskTutorialApp/app/views.py', reloading * Restarting with stat 2020-06-02 14:59:49,592:INFO:werkzeug: * Restarting with stat * Debugger is active! * Debugger PIN: 150-849-897
Presently check the stack follow in your program and go to the last line. Click it to grow its view and snap the CLI symbol to open a shell in intuitive mode.
Once opened, you will see that the program prompts you to enter your troubleshoot PIN. Enter the investigate PIN and snap OK.
As we continue on in the wake of giving the troubleshoot PIN, we can get to the intelligent shell.
We access the shell from inside the program and can really take a look at variable qualities to track down the reason for the special case and better handle the blunder. Kindly investigate one of the models displayed in the image beneath.
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