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On this article, we’ll introduce Flask, a preferred microframework for Python that provides an alternative choice to the enormous that’s Django.
Flask is designed to be light-weight and versatile, permitting builders to create internet apps shortly and simply. On this article, we’ll cowl what Flask is, its key options, the advantages of its easy API, its flexibility in supporting third-party extensions, the most typical Flask extensions, and when is and isn’t an excellent time to make use of Flask.
What Is Flask?
Flask is a micro internet framework written in Python that’s used for creating internet purposes. It’s constructed on a easy philosophy of retaining issues easy and light-weight, giving builders solely a very powerful instruments wanted to construct internet apps with out pointless complexity.
It’s constructed on prime of the Werkzeug WSGI toolkit, which supplies internet server performance wanted for dealing with requests and responses, and the Jinja2 templating engine, which supplies Flask the flexibility to deal with HTML templates, permitting builders to create dynamic internet purposes.
Listed below are a few of the key options of Flask that make it such an ideal framework to work with:
- It has a easy API for creating internet routes and dealing with requests.
- The Jinja templating engine gives help for HTML templates, permitting builders to create internet pages simply.
- It’s extremely extendable, as a result of its help for third-party extensions, so a developer can set up extensions relying on their undertaking wants.
- It comes bundled with a growth server that makes it straightforward to check and debug apps.
Total, Flask supplies a strong, versatile, but easy framework for constructing internet purposes. It’s a sensible choice for each new and skilled internet builders, and is among the hottest internet frameworks within the Python internet growth ecosystem.
Benefits of Flask
Let’s now take a extra detailed have a look at a few of the benefits of utilizing Flask in growth.
Simplicity. Flask’s design philosophy emphasizes simplicity, which makes it straightforward for builders at any degree to grasp and use. This additionally implies that builders have a really minimal studying curve, since they solely have to study a number of ideas and APIs to get began constructing internet purposes.
Flexibility. The micro nature of Flask — offering solely the core options of an internet framework — provides builders the ability to customise and prolong it to swimsuit their necessities utilizing Flask extensions or third-party libraries.
Documentation. The Flask documentation may be very complete, with good protection of primary to superior subjects, making it very straightforward for builders to discover ways to use the framework.
Compatibility. Flask is appropriate with a variety of Python variations, which makes it straightforward to make use of with current Python codebases. It additionally has help for a number of internet servers, which makes it straightforward to deploy it on quite a lot of internet hosting platforms.
Fast growth. Flask’s simplicity and adaptability cut back the boilerplate wanted to arrange an software, permitting builders to get began shortly.
Across the Internet, Flask is utilized in numerous fascinating methods. Just a few notable examples are:
- PgAdmin. The Postgres admin interface runs on a Flask occasion, giving builders an interface the place they’ll handle their Postgres databases.
- Twilio. This can be a communication platform that makes use of Flask in a number of of its APIs.
- Pinterest. This photo-sharing app makes use of Flask within the internet growth stack, permitting its crew to create some customized options and integrations simply.
When to Use Flask
Flask’s simplicity and ease of use make it a superb selection for a variety of internet tasks:
- Prototyping. Its ease of use and adaptability make it a superb selection for shortly creating prototypes permitting builders to construct and check new options quick.
- Creating RESTful APIs. Its personal easy API makes it straightforward to create and deal with HTTP requests.
- Ecommerce apps. It really works effectively for constructing on-line marketplaces and ecommerce platforms.
- Finance. It’s helpful for constructing monetary purposes, with account administration, transaction processing, and funding monitoring.
- AI. It gives a helpful and easy approach to construct and deploy AI coaching fashions.
When Not To Use Flask
Whereas Flask is a superb framework and has a number of benefits and nice options, there are conditions these options work towards it. Let’s discover a few of the tasks that swimsuit different kinds of frameworks higher.
Initiatives that require built-in performance. Being a microframework, Flask solely supplies the core bits wanted to create an internet software. If a undertaking requires, say, an admin interface, authentication, or an ORM, then Django is a greater choice.
Initiatives with strict safety necessities. As Flask is a versatile framework, we’ve to depend on third-party extensions to implement some degree of safety in our apps. Whereas this actually works, it’s higher to depend on a extra battle-tested framework that takes a safer strategy, reminiscent of Twister or Twisted.
Initiatives that implement some coding commonplace. As a result of Flask’s flexibility, creating purposes on it leaves builders to make apps in any manner they see match. Nevertheless, frameworks like Django make sure that builders observe a specific conference, which means that builders can transfer from one undertaking to different simply.
Setting Up a Flask Improvement Setting
Let’s now have a look at easy methods to get began with Flask, from organising the event surroundings, to set up, and eventually spinning up a minimal software.
Stipulations
Python needs to be put in on the event machine. Listed below are directions for that (though we might have already got it put in).
Create a Digital Setting
A digital surroundings is an remoted Python surroundings the place we are able to set up packages for a given undertaking with out affecting the worldwide Python set up. (Right here’s additional dialogue about why digital environments are helpful.) There are completely different packages for creating digital environments in Python, reminiscent of virtualenv, venv, or Conda.
On this article, we’ll use virtualenv. We are able to set up it with the next command:
pip set up virtualenv
As soon as virtualenv has been put in, we are able to create a listing the place our Flask software will reside. We are able to name the listing no matter we would like — apart from Flask, as that can trigger conflicts. We’ll name ours flask_intro:
mkdir flask_intro
Subsequent, grow to be that listing in order that we are able to begin utilizing it:
cd flask_intro
In that listing, let’s now create our digital surroundings, utilizing the next command:
virtualenv myenv
The command above creates a digital surroundings and calls it myenv. Let’s activate it in order that we are able to set up Flask in it. To activate the digital surroundings on Linux or macOS, use the next command:
. myenv/bin/activate
On Home windows, use this command:
. myenvScriptsactivate
As soon as our digital surroundings has been activated, it can present the identify of the digital surroundings on the shell immediate, just like the output under:
(myenv)/~(path to your undertaking listing)$
Inside our activated digital surroundings, we are able to go forward and set up Flask, utilizing the next command:
pip set up Flask
As soon as Flask finishes putting in, let’s go forward and create a minimal software. We’ll create a module that can maintain our Flask software. For simplicity’s sake, let’s name it good day.py. On Linux or macOS we are able to use the next command to create the file in our flask_intro listing:
contact good day.py
The command above creates a file named good day.py. We might additionally use a growth surroundings to create the file. As soon as the file has been created, put the under code in it and reserve it:
from flask import Flask
app = Flask(__name__)
@app.route("https://www.sitepoint.com/")
def hello_world():
return 'Hey, World!'
Within the code above, we import the Flask class from the flask module, then create an occasion of Flask that we name app and go the __name__ variable.
Then we’ve the route decorator @app.route(“”), which implies that the hello_world() operate can be triggered when somebody visits the foundation route of our software as soon as it’s run.
There are numerous ways in which we might run the applying, so let’s have a look at a few of them. The primary manner is to produce the flask command with various arguments: --app, then the identify of the module that holds, our Flask software, after which run. See under:
flask –app <the identify of your module> run
Utilizing the instance above to run our pattern software:
flask –app good day run
That can run our software on the default port 5000 so the applying can be out there on http://localhost:5000/ or at http://127.0.0.1:5000/. If we would like the applying to be out there on a distinct port, we are able to specify the port utilizing -p or --port choice. For instance:
flask --app good day run --port=8080
That can run the server on port 8080. The opposite manner we are able to run the applying is by simply utilizing the flask run instructions. Nevertheless, for us to have the ability to do this, we have to inform Flask the identify of the module that can maintain the Flask occasion, and we do this by setting the FLASK_APP surroundings variable. So in our case, the Flask software is contained in a file named good day.py. So we are able to set it this fashion:
export FLASK_APP=good day
Now that we’ve set the FLASK_APP surroundings variable, we are able to run the event server like so:
flask run
With that code, we now have an internet software operating. This demonstrates the core philosophy of Flask: we don’t want numerous boilerplate code to get issues going. Nevertheless, the applying we’ve arrange above isn’t very purposeful or helpful, because it solely renders the string “Hey World!” on our internet web page. To do something extra helpful, we are able to flip to templates. We’ll have a look at easy methods to deal with them subsequent.
Flask Templates
Flask templates are a approach to create dynamic internet pages that may show completely different content material based mostly on numerous elements, reminiscent of information from a database, or person enter. Templates in Flask are a mix of HTML and particular placeholders known as template variables which are changed with precise values at runtime.
Templates are saved within the templates listing. So to make use of templates, we have to import the render_template() technique from flask. The render_template() technique takes a template identify and any non-obligatory information that must be handed to the template.
Let’s see an instance of a operate that makes use of a template to render an internet web page:
from flask import Flask, render_template
app = Flask(__name__)
@app.route("https://www.sitepoint.com/")
def index():
title = 'Welcome to my web site!'
message = 'That is an instance of utilizing Flask templates.'
return render_template('index.html', title=title, message=message)
Within the instance above, we’ve a view operate — index() — that’s certain to the foundation URL (“/”) by the @app.route() decorator. The operate has two variables, title and message. Lastly, we go the template index.html to the render_template(), along with the title and message variables.
For the code above to work, we have to have an index.html template residing in a templates listing. So the template will look one thing like this:
# index.html
<!doctype html>
<html>
<head>
<title>{{ title }}</title>
</head>
<physique>
<h1>{{ title }}</h1>
<p>{{ message }}</p>
</physique>
</html>
Within the index.html file, the placeholders {{title}} and {{ message }} are changed with the values handed to the template within the render_template() technique.
Templates can even embrace extra complicated logic reminiscent of if statements and for loops, which permit for extra dynamic pages to be generated.
So templates in Flask present builders with a really highly effective choice for creating dynamic internet pages wealthy with user-generate info.
Flask Routing
Most internet purposes could have multiple URL, so we have to have a manner of realizing which operate handles which URL. In Flask, this mapping is called routing — the method of binding or mapping URLs to view capabilities. Binding URLs to view capabilities permits the applying to deal with various kinds of requests, reminiscent of GET, POST, PUT, DELETE, and extra. It additionally permits the applying to deal with a number of requests from completely different purchasers.
To arrange routes in Flask, we use the route() decorator. The decorator binds a URL to a view operate — so when a person visits a URL that exists on our software, Flask triggers the related view operate to deal with the request.
Let’s see an instance:
from flask import Flask, render_template
app = Flask(__name__)
@app.route("/about")
def about():
return "That is the about web page"
Within the instance above, we outline an about URL (/about). When the applying receives a request for the about URL, Flask calls the about() operate, which returns the string “That is the about web page”.
To date, though these examples return completely different pages, all of them simply use the GET HTTP request. So as to have the ability to deal with any particular request, we are able to specify the HTTP technique as an non-obligatory argument to the route() decorator.
Let’s see an instance of a PUT request:
from flask import Flask, request
app = Flask(__name__)
@app.route('/customers/<int:user_id>', strategies=['PUT'])
def update_user(user_id):
information = request.get_json()
return {'message': f'Consumer {user_id} up to date efficiently'}, 200
On this instance, we outline a route that handles a PUT request to replace person particulars given their user_id. We use <int:user_id> within the route to point that the person ID ought to be an integer.
Within the update_user() operate, we get the person information from the request physique utilizing the request.get_json() technique. We do one thing with the person information, reminiscent of updating the person within the database, after which return a response indicating success or failure together with an HTTP standing code (a 200 on this case to indicate success).
Total, routing permits Flask to have the ability to deal with various kinds of requests and permits our software to deal with and act on information in another way, relying on the URL {that a} person visits.
Flask Kinds and Validation
Other than displaying information for customers, Flask templates can even take enter from customers for additional processing or storage. For that, Flask supplies built-in help for processing HTML types and dealing with person enter. Flask types are based mostly on the WTForms library, which supplies a versatile and highly effective approach to deal with type information and carry out validations. Nevertheless, the library isn’t part of the usual Flask set up, so we have to set up it utilizing the next command:
pip set up WTForms
As soon as we’ve put in WTForms, to make use of types in Flask we have to outline a type class that can inherit from flask_wtf.FlaskForm. The category will comprise the fields which are going to be on the shape and any validation guidelines that ought to be utilized to them.
Let’s see an instance of a login type:
from flask_wtf import FlaskForm
from wtforms import StringField, PasswordField, SubmitField
from wtforms.validators import DataRequired, E-mail, Size
class LoginForm(FlaskForm):
e mail = StringField('E-mail', validators=[DataRequired(), Email()])
password = PasswordField('Password', validators=[DataRequired(), Length(min=6)])
submit = SubmitField('Log In')
Within the instance above, we outline a login type with two fields — e mail and password — and a submit button. We even have a validators argument that’s used to specify validation guidelines for every area. For instance, on this case we require the e mail area to comprise a legitimate e mail deal with and the password area to comprise a password of no fewer than six characters.
As soon as we’ve outlined the shape class, we are able to use it within the login view operate to render the shape and course of the shape information submitted by the person. Let’s see an instance of the view operate:
from flask import render_template, request
from .types import LoginForm
@app.route('/login', strategies=['GET', 'POST'])
def login():
type = LoginForm()
if type.validate_on_submit():
e mail = type.e mail.information
password = type.password.information
return render_template('login.html', type=type)
Within the instance above, we’ve a login view that accepts two HTTP strategies (GET and POST), so when customers entry the URL from a browser the LoginForm is rendered as an HTML type utilizing the render_template technique, and when a person submits the shape we verify if the shape is legitimate utilizing the validate_on_submit technique. If the shape is legitimate, we entry the e-mail and password.
The login.html type might look one thing like this:
# login.html
<h1>Login</h1>
<type technique="POST">
{{ type.csrf_token }}
<div>
{{ type.e mail.label }} {{ type.e mail() }}
{% for error in type.e mail.errors %}
<span fashion="colour: purple;">[{{ error }}]</span>
{% endfor %}
</div>
<div>
{{ type.password.label }} {{ type.password() }}
{% for error in type.password.errors %}
<span fashion="colour: purple;">[{{ error }}]</span>
{% endfor %}
</div>
{{ type.submit() }}
</type>
The above template will render the e mail and password fields, together with their labels, and a submit button with the textual content “Login”. The type.csrf_token area is included to stop cross-site request forgery (CSRF) assaults. The {% for %} loops are used to show any validation errors that will happen.
Through the use of Flask types, we’ve a strong manner of dealing with person enter, and we’ll have the ability to validate the info they enter.
Flask Extensions
As we’ve seen, Flask is a microframework that solely consists of a very powerful components wanted to create an internet software. Nevertheless, if we have to add performance that isn’t supplied out of the field by Flask, we have to add packages to the set up. Flask extensions are the way in which we offer this extra performance. We are able to merely set up the package deal we’d like. There are numerous extensions made by the Flask group.
Listed below are a few of the hottest ones:
- Flask-SQLAlchemy: supplies integration with the SQLAlchemy toolkit that makes it straightforward to work together with databases.
- Flask-Login: supplies person authentication and session administration to Flask.
- Flask-Mail: supplies a easy interface to ship emails from Flask.
There are tons of of extensions made by the Flask group to deal with completely different performance. Utilizing the extensions is mostly simple. First, we have to set up the extension we would like utilizing pip.
Let’s see an instance of utilizing Flask-SQLAlchemy. First, we have to set up it:
pip set up flask-sqlalchemy
Subsequent, we have to configure it. For instance:
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///instance.db'
db = SQLAlchemy(app)
class Consumer(db.Mannequin):
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(80), distinctive=True, nullable=False)
e mail = db.Column(db.String(120), distinctive=True, nullable=False)
def __repr__(self):
return '<Consumer %r>' % self.username
Within the instance above, we’ve a Consumer mannequin with a username and e mail area. We additionally configure SQLALCHEMY_DATABASE_URI, indicating that we’re utilizing an SQLite database positioned at instance.db. With that set, we now have entry to the db object that permits us to work together with the database. For instance, we might create a brand new person and add it to the database, like so:
from app import db, Consumer
person = Consumer(username='john', e mail='john@instance.com')
db.session.add(person)
db.session.commit()
With Flask extensions, our software is ready to have extra performance than it might usually have with the core Flask implementation.
Conclusion
On this article, we launched Flask, a light-weight and versatile internet framework for Python. We mentioned some great benefits of utilizing Flask for internet growth, together with its simplicity, flexibility, and ease of use. We additionally coated easy methods to arrange a growth surroundings, create routes, use templates, deal with types, and use extensions like Flask-SQLAlchemy.
To summarize, Flask is a superb selection for constructing internet purposes of any measurement, from small private tasks to large-scale business purposes. It’s straightforward to study and use, but additionally gives superior options by way of its many extensions.
In case you’re interested by studying extra about Flask, listed below are some extra assets:
In case you’d wish to study extra about Django and Flask and their greatest use circumstances, take a look at Python Internet Improvement with Django and Flask.
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