Python is a versatile language that can be used for backend development with frameworks like Django and Flask. In this article, we will take a look at these two frameworks and see how they can be used to develop Python applications.
Django is a high-level web framework that is written in Python. It is designed to make the development process of web applications easier and faster. Django comes with a lot of features out-of-the-box, such as a user authentication system, an object-relational mapper (ORM), and a template engine.
Django is a good choice for large and complex applications. It is also suitable for projects that require a high level of security.
To use Django, you need to install it first. You can do this using the pip package manager:
pip install django
Once Django is installed, you can create a new project using the django-admin command:
django-admin startproject myproject
This will create a new directory called myproject with the following file structure:
myproject/
├── manage.py
└── myproject
├── __init__.py
├── settings.py
├── urls.py
└── wsgi.py
The manage.py file is used to manage your Django project. The other files in the myproject directory are settings files.
Applications are the building blocks of Django projects. A project can have multiple applications and each application can have different functionality.
To create a new application, use the django-admin command:
django-admin startapp myapp
This will create a new directory called myapp with the following file structure:
myapp/
├── __init__.py
├── admin.py
├── apps.py
├── models.py
├── tests.py
└── views.py
The myapp directory contains all the files for your application. The models.py file is used to define the data models for your application. The views.py file is used to define the views (i.e. the logic) for your application. The urls.py file is used to define the URLs for your application.
Models are the core of Django applications. Models are used to represent the data in your application.
A model is a Python class that inherits from the django.db.models.Model class. Each model has a number of fields, which are used to represent the data in your application.
For example, if you were building a blog application, you might have a Post model with the following fields:
class Post(models.Model):
title = models.CharField(max_length=255)
body = models.TextField()
published_at = models.DateTimeField(auto_now_add=True)
The Post model has three fields: title, body, and published_at. The title and body fields are used to store the title and body of the blog post, respectively. The published_at field is used to store the date and time when the blog post was published.
After you have defined your models, you need to register them with Django. You can do this by adding the following line to the admin.py file:
admin.site.register(Post)
This will register the Post model with the Django admin site.
Views are the logic of Django applications. They are used to handle the incoming HTTP requests and return the HTTP responses.
Views are Python functions that take an HttpRequest object as an argument and return an HttpResponse object.
For example, if you were building a blog application, you might have a view that displays a list of all the blog posts:
def post_list(request):
posts = Post.objects.all()
return render(request, 'post_list.html', {'posts': posts})
The post_list view takes an HttpRequest object and returns an HttpResponse object. The HttpResponse object contains the HTML for the page that will be displayed.
The post_list view gets all the Post objects from the database and passes them to the post_list.html template. The post_list.html template renders the HTML for the page.
URLs are used to map views to specific URLs. They are defined in the urls.py file.
For example, if you were building a blog application, you might have the following urls.py file:
from django.conf.urls import url
from . import views
urlpatterns = [
url(r'^$', views.post_list, name='post_list'),
]
The urlpatterns variable is a list of URL patterns. Each URL pattern is a tuple of the following:
The ^$ regular expression matches the empty string. This URL pattern will match the / URL.
When the / URL is requested, the post_list view function will be called. The post_list view function will return the HTML for the page.
The name of the URL is used to identify the URL. This is useful for reversing URLs (i.e. generating URLs from view functions).
Templates are used to render the HTML for Django views. Django comes with a built-in template engine, called the Django template engine.
The Django template engine takes a template and a context (a Python dictionary) and renders the template with the context data.
The template is rendered with the render function:
def post_list(request):
posts = Post.objects.all()
return render(request, 'post_list.html', {'posts': posts})
The render function takes the request object, the name of the template, and the context data. The render function returns the HTML for the page.
The post_list.html template might look like this:
<html>
<head>
<title>My Blog</title>
</head>
<body>
{% for post in posts %}
<h1>{{ post.title }}</h1>
<p>{{ post.body }}</p>
{% endfor %}
</body>
</html>
The post_list.html template loops through the posts variable and displays the title and body of each Post.
Flask is a microframework for Python. It is designed to make the development process of web applications easier and faster. Flask comes with a few features out-of-the-box, such as a development server and a basic template engine.
Flask is a good choice for small and simple applications. It is also suitable for projects that require a high level of flexibility.
To use Flask, you need to install it first. You can do this using the pip package manager:
pip install flask
Once Flask is installed, you can create a new file called app.py with the following code:
from flask import Flask
app = Flask(__name__)
@app.route('/')
def index():
return 'Hello, World!'
if __name__ == '__main__':
app.run()
This code will create a new Flask application. The @app.route decorator is used to map URLs to view functions. The index view function returns the string Hello, World!.
The if __name__ == '__main__': block is used to run the application. The app.run function will start a development server.
You can run the application using the python command:
python app.py
You can access the application at http://localhost:5000/.
Applications are the building blocks of Flask projects. A project can have multiple applications and each application can have different functionality.
To create a new application, create a new file called app.py with the following code:
from flask import Flask
app = Flask(__name__)
This code will create a new Flask application.
Views are the logic of Flask applications. They are used to handle the incoming HTTP requests and return the HTTP responses.
Views are Python functions that take an HttpRequest object as an argument and return an HttpResponse object.
For example, if you were building a blog application, you might have a view that displays a list of all the blog posts:
@app.route('/')
def post_list():
posts = Post.objects.all()
return render_template('post_list.html', {'posts': posts})
The post_list view takes an HttpRequest object and returns an HttpResponse object. The HttpResponse object contains the HTML for the page that will be displayed.
The post_list view gets all the Post objects from the database and passes them to the post_list.html template. The post_list.html template renders the HTML for the page.
URLs are used to map views to specific URLs. They are defined in the app.py file.
For example, if you were building a blog application, you might have the following app.py file:
@app.route('/')
def post_list():
...
@app.route('/posts/<int:post_id>')
def post_detail(post_id):
...
The @app.route decorator is used to map URLs to view functions. The post_list view function will be called when the / URL is requested. The post_detail view function will be called when the /posts/<int:post_id> URL is requested.
Templates are used to render the HTML for Flask views. Flask comes with a built-in template engine, called the Jinja2 template engine.
The Jinja2 template engine takes a template and a context (a Python dictionary) and renders the template with the context data.
The template is rendered with the render_template function:
@app.route('/')
def post_list():
posts = Post.objects.all()
return render_template('post_list.html', {'posts': posts})
The render_template function takes the name of the template and the context data. The render_template function returns the HTML for the page.
The post_list.html template might look like this:
<html>
<head>
<title>My Blog</title>
</head>
<body>
{% for post in posts %}
<h1>{{ post.title }}</h1>
<p>{{ post.body }}</p>
{% endfor %}
</body>
</html>
The post_list.html template loops through the posts variable and displays the title and body of each Post.
In this article, we have looked at two Python frameworks for backend development: Django and Flask. We have seen how to get started with each framework and how to create a basic application.