Chapter 2: Hello World app
In this chapter we’ll build a Django project that simply says “Hello, World” on the homepage. This is the traditional way to start a new programming language or framework. We’ll also work with Git for the first time and deploy our code to GitHub.
If you become stuck at any point, complete source code for this and all future chapters is available online on the official GitHub repo.
Initial Set Up
To begin, navigate to a new directory on your computer. For example, we can create a
helloworld folder on the Desktop with the following commands.
$ cd ~/Desktop $ mkdir helloworld && cd helloworld
Make sure you’re not already in an existing virtual environment at this point. If you see text in parentheses
() before the dollar sign (
$) then you are. To exit it, type
exit and hit
Return. The parentheses should disappear which means that virtual environment is no longer active.
pipenv to create a new virtual environment, install Django, and then activate it.
$ pipenv install django~=3.1.0 $ pipenv shell
If you are on a Mac you should see parentheses now at the beginning of your command line prompt in the form
(helloworld). If you are on Windows you will not see a visual prompt at this time.
Create a new Django project called
config making sure to include the period (
.) at the end of the command so that it is installed in our current directory.
(helloworld) $ django-admin startproject config .
If you use the
tree command you can see what our Django project structure now looks like. (Note: If
tree doesn’t work for you, install it with Homebrew:
brew install tree.)
(helloworld) $ tree . ├── Pipfile ├── Pipfile.lock ├── config │ ├── __init__.py | ├── asgi.py │ ├── settings.py │ ├── urls.py │ └── wsgi.py └── manage.py 1 directory, 8 files
config/settings.py file controls our project’s settings,
urls.py tells Django which pages to build in response to a browser or URL request, and
wsgi.py, which stands for Web Server Gateway Interface, helps Django serve our eventual web pages. The
manage.py file is used to execute various Django commands such as running the local web server or creating a new app. Last, but not least, is the
asgi.py file, new to Django as of version 3.0 which allows for an optional Asynchronous Server Gateway Interface to be run.
Django comes with a built-in web server for local development purposes which we can now start with the
(helloworld) $ python manage.py runserver
If you visit http://127.0.0.1:8000/ you should see our familiar Django welcome page.
Note that the full command line output will contain additional information including a warning about
18 unapplied migrations.
Watching for file changes with StatReloader Performing system checks... System check identified no issues (0 silenced). You have 18 unapplied migration(s). Your project may not work properly until you apply the migrations for app(s): admin, auth, contenttypes, sessions. Run 'python manage.py migrate' to apply them. August 3, 2020 - 14:57:42 Django version 3.1, using settings 'config.settings' Starting development server at http://127.0.0.1:8000/ Quit the server with CONTROL-C.
Technically this warning doesn’t matter at this point. Django is complaining that we have not yet “migrated,” or configured, our initial database. Since we won’t actually use a database in this chapter, the warning won’t affect the end result.
However, since warnings are still annoying to see, we can remove it by first stopping the local server with the
Control+c command and then running
python manage.py migrate.
$ python manage.py migrate Operations to perform: Apply all migrations: admin, auth, contenttypes, sessions Running migrations: Applying contenttypes.0001_initial... OK Applying auth.0001_initial... OK Applying admin.0001_initial... OK Applying admin.0002_logentry_remove_auto_add... OK Applying admin.0003_logentry_add_action_flag_choices... OK Applying contenttypes.0002_remove_content_type_name... OK Applying auth.0002_alter_permission_name_max_length... OK Applying auth.0003_alter_user_email_max_length... OK Applying auth.0004_alter_user_username_opts... OK Applying auth.0005_alter_user_last_login_null... OK Applying auth.0006_require_contenttypes_0002... OK Applying auth.0007_alter_validators_add_error_messages... OK Applying auth.0008_alter_user_username_max_length... OK Applying auth.0009_alter_user_last_name_max_length... OK Applying auth.0010_alter_group_name_max_length... OK Applying auth.0011_update_proxy_permissions... OK Applying auth.0012_alter_user_first_name_max_length... OK Applying sessions.0001_initial... OK
What Django has done here is migrate the built-in apps provided for us which we’ll cover properly later in the book. But now, if you execute
python manage.py runserver again, you should see the following clean output on the command line:
$ python manage.py runserver Watching for file changes with StatReloader Performing system checks... System check identified no issues (0 silenced). August 3, 2020 - 15:23:14 Django version 3.1, using settings 'config.settings' Starting development server at http://127.0.0.1:8000/ Quit the server with CONTROL-C.
Create An App
Django uses the concept of projects and apps to keep code clean and readable. A single Django project contains one or more apps within it that all work together to power a web application. This is why the command for a new Django project is
For example, a real-world Django e-commerce site might have one app for user authentication, another app for payments, and a third app to power item listing details: each focuses on an isolated piece of functionality. That’s three distinct apps that all live within one top-level project.
How and when you split functionality into apps is somewhat subjective, but in general, each app should have a clear function.
Now it’s time to create our first app. From the command line, quit the server with
Control+c. Then use the
startapp command followed by the name of our app, which will be
(helloworld) $ python manage.py startapp pages
If you look again inside the directory with the
tree command you’ll see Django has created a
pages directory with the following files:
(helloworld) $ tree ├── pages │ ├── __init__.py │ ├── admin.py │ ├── apps.py │ ├── migrations │ │ └── __init__.py │ ├── models.py │ ├── tests.py │ └── views.py
Let’s review what each new
pages app file does:
admin.pyis a configuration file for the built-in Django Admin app
apps.pyis a configuration file for the app itself
migrations/keeps track of any changes to our
models.pyfile so our database and
models.pystay in sync
models.pyis where we define our database models which Django automatically translates into database tables
tests.pyis for our app-specific tests
views.pyis where we handle the request/response logic for our web app
Even though our new app exists within the Django project, Django doesn’t “know” about it until we explicitly add it. In your text editor, open the
settings.py file and scroll down to
INSTALLED_APPS where you’ll see six built-in Django apps already there. Add our new
pages app at the bottom:
# config/settings.py INSTALLED_APPS = [ 'django.contrib.admin', 'django.contrib.auth', 'django.contrib.contenttypes', 'django.contrib.sessions', 'django.contrib.messages', 'django.contrib.staticfiles', 'pages', # new ]
Don’t worry if you are confused at this point: it takes practice to internalize how Django projects and apps are structured. Over the course of this book we will build many projects and apps and the patterns will soon become familiar.
URLs, Views, Models, Templates
In Django, at least three (often four) separate files are required to power one single page. Within an app these are the
urls.py file, the
views.py file, the
models.py file, and finally an HTML template such as
This interaction is fundamental to Django yet very confusing to newcomers so let’s map out the order of a given HTTP request/response cycle. When you type in a URL, such as
https://djangoforbeginners.com, the first thing that happens within our Django project is a URLpattern is found that matches the homepage. The URLpattern specifies a view which then determines the content for the page (usually from a database model) and then ultimately a template for styling and basic logic. The end result is sent back to the user as an HTTP response.
The complete flow looks something like this:
URL -> View -> Model (typically) -> Template
Remember how I said it can take three or four files for a given page? That’s because a model is not always needed, in which case three files are enough. But generally speaking four will be used as we’ll see later in this book.
The main takeaway here is that in Django views determine what content is displayed on a given page while URLConfs determine where that content is going. The model contains the content from the database and the template provides styling for it.
When a user requests a specific page, like the homepage, the urls.py file uses a regular expression to map that request to the appropriate view function which then returns the correct data. In other words, our view will output the text “Hello, World” while our url will ensure that when the user visits the homepage they are redirected to the correct view.
To see this in action, let’s start by updating the
views.py file in our
pages app to look as follows:
# pages/views.py from django.http import HttpResponse def homePageView(request): return HttpResponse('Hello, World!')
Basically, we’re saying whenever the view function
homePageView is called, return the text “Hello, World!” More specifically, we’ve imported the built-in
HttpResponse method so we can return a response object to the user. We’ve created a function called
homePageView that accepts the
request object and returns a
response with the string “Hello, World!”
Now we need to configure our urls. Within the
pages app, create a new
urls.py file which on a Mac can be done with the
touch command; Windows users must create the file within a text editor.
(helloworld) $ touch pages/urls.py
Then update it with the following code:
# pages/urls.py from django.urls import path from .views import homePageView urlpatterns = [ path('', homePageView, name='home') ]
On the top line we import
path from Django to power our
URLpattern and on the next line we import our views. By referring to the
views.py file as
.views we are telling Django to look within the current directory for a
views.py file and import the view
homePageView from there.
Our URLpattern has three parts:
- a Python regular expression for the empty string
- a reference to the view called
- an optional named URL pattern called
In other words, if the user requests the homepage, represented by the empty string
'', then use the view called
We’re almost done at this point. The last step is to update our
config/urls.py file. It’s common to have multiple apps within a single Django project, like
pages here, and they each need their own dedicated URL path.
Update the existing
config/urls.py file as follows:
# config/urls.py from django.contrib import admin from django.urls import path, include # new urlpatterns = [ path('admin/', admin.site.urls), path('', include('pages.urls')), # new ]
include on the second line next to
path and then created a new urlpattern for our
pages app. Now whenever a user visits the homepage they will first be routed to the
pages app and then to the
This need for two separate
urls.py files is often confusing to beginners. Think of the top-level
config/urls.py as the gateway to various url patterns distinct to each app.
We have all the code we need now. To confirm everything works as expected, restart our Django server:
(helloworld) $ python manage.py runserver
If you refresh the browser for http://127.0.0.1:8000/ it now displays the text “Hello, world!”
In the previous chapter we also installed git which is a version control system. Let’s use it here. The first step is to initialize (or add) git to our repository.
(helloworld) $ git init
If you then type
git status you’ll see a list of changes since the last git commit. Since this is our first commit, this list is all of our changes so far.
(helloworld) $ git status On branch master No commits yet Untracked files: (use "git add <file>..." to include in what will be committed) Pipfile Pipfile.lock db.sqlite3 config/ manage.py pages/ nothing added to commit but untracked files present (use "git add" to track)
We next want to add all changes by using the command
add -A and then
commit the changes along with a message (
-m) describing what has changed.
(helloworld) $ git add -A (helloworld) $ git commit -m 'initial commit'
Please note Windows users may receive an error git commit error: pathspec ‘commit’ did not match any file(s) known to git which appears to be related to using single quotes
'' as opposed to double quotes
"". If you see this error, using double quotes for all commit messages going forward.
It’s a good habit to create a remote repository of your code for each project. This way you have a backup in case anything happens to your computer and more importantly, it allows for collaboration with other software developers. Popular choices include GitHub, Bitbucket, and GitLab. When you’re learning web development, it’s best to stick to private rather than public repositories so you don’t inadvertently post critical information such as passwords online.
We will use GitHub in this book but all three services offer similar functionality for newcomers. Sign up for a free account on GitHub’s homepage and verify your email address. Then navigate to the “Create a new repository” page located at https://github.com/new.
Enter the repository name
hello-world and click on the radio button next to “Private” rather than “Public.” Then click on the button at the bottom for “Create Repository.”
Your first repository is now created! However there is no code in it yet. Scroll down on the page to where it says “…or push an existing repository from the command line.” That’s what we want.
Copy the text immediately under this headline and paste it into your command line. Note that my username is
wsvincent here; yours will be different so if you copy my snippet below it won’t work! This syncs the local directory on our computer with the remote repository on the GitHub website.
(helloworld) $ git remote add origin https://github.com/wsvincent/hello-world.git
The last step is to “push” our code to GitHub.
(helloworld) $ git push -u origin master
Hopefully this command works and you can go back to your GitHub page and refresh it to see your local code now hosted online.
Unfortunately, there is a good chance that the last command yielded an error if you are a new developer and do not have SSH keys already configured.
ERROR: Repository not found. fatal: Could not read from remote repository. Please make sure you have the correct access rights and the repository exists.
This cryptic message means we need to configure SSH keys. This is a one-time thing but a bit of a hassle to be honest.
SSH is a protocol used to ensure private connections with a remote server. Think of it as an additional layer of privacy on top of username/password. The process involves generating unique SSH keys and storing them on your computer so only GitHub can access them.
First, check whether you have existing SSH keys. Github has a guide to this that works for Mac, Windows, and Linux. If you don’t have existing public and private keys, you’ll need to generate them. GitHub, again, has a guide on doing this.
Once complete you should be able to execute the
git push -u origin master command successfully!
It’s normal to feel overwhelmed and frustrated if you become stuck with SSH keys. GitHub has a lot of resources to walk you through it but the reality is its very intimidating the first time. If you’re truly stuck, continue with the book and come back to SSH Keys and GitHub with a full nights sleep. I can’t count the number of times a clear head has helped me process a difficult programming issue.
Assuming success with GitHub, go ahead and exit our virtual environment with the
(helloworld) $ exit
You should now see no parentheses on your command line, indicating the virtual environment is no longer active.
Congratulations! We’ve covered a lot of fundamental concepts in this chapter. We built our first Django application and learned about Django’s project/app structure. We started to learn about views, urls, and the internal Django web server. And we worked with git to track our changes and pushed our code into a private repo on GitHub.
Continue on to Chapter 3: Pages App where we’ll build and deploy a more complex Django application using templates and class-based views.