Chapter 2: Hello World app
In this chapter we’ll build a new Django project that 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 which is a version control system and deploy our code to Bitbucket, a remote code repository.
To start 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 The parentheses should disappear which means that virtual environment is no longer active.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 $ pipenv shell
If you are on a Mac you should see parentheses now at the beginning of your command line prompt in the form
XXX represents random characters. On my computer I see
(helloworld-415ivvZC). I’ll display
(helloworld) here in the text but you will see something slightly different on your computer. If you are on Windows you will not see a visual prompt at this time.
Create a new Django project called
helloworld_project 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 helloworld_project .
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 . ├── helloworld_project │ ├── __init__.py │ ├── settings.py │ ├── urls.py │ └── wsgi.py └── manage.py 1 directory, 5 files
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 last file
manage.py is used to execute various Django commands such as running the local web server or creating a new app.
Django comes with a built-in web server for local development purposes. We can start it with the
(helloworld) $ python manage.py runserver
If you visit http://127.0.0.1:8000/ you should see our familiar Django welcome page.
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
startproject! 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.
We need to create our first app which we’ll call
pages. From the command line, quit the server with
Control+c. Then use the
(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
├── 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:
# helloworld_project/settings.py INSTALLED_APPS = [ 'django.contrib.admin', 'django.contrib.auth', 'django.contrib.contenttypes', 'django.contrib.sessions', 'django.contrib.messages', 'django.contrib.staticfiles', 'pages', # new ]
Views and URLConfs
In Django, Views determine what content is displayed on a given page while URLConfs determine where that content is going.
When a user requests a specific page, like the homepage, the URLConf 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.
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. Our function
homePageView accepts the
and returns a response with the string
Now we need to configure our urls. Within the
pages app, create a new
(helloworld) $ touch pages/urls.py
Then update it with the following code:
# pages/urls.py from django.urls import path from . import views urlpatterns = [ path('', views.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. The period used here
from . import views means reference the current directory, which is our
pages app containing both
urls.py. Our urlpattern has three parts:
- a Python regular expression for the empty string
- specify the view which is called
- add an optional url name of
In other words, if the user requests the homepage, represented by the empty string
'' then use the view called
We’re almost done. The last step is to configure our project-level
urls.py file too. Remember that it’s common to have multiple apps within a single Django project, so they each need their own route.
helloworld_project/urls.py file as follows:
# helloworld_project/urls.py from django.contrib import admin from django.urls import path, include urlpatterns = [ path('admin/', admin.site.urls), path('', include('pages.urls')), ]
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 at
/ they will first be routed to the
pages app and then to the
It’s often confusing to beginners that we don’t need to import the
pages app here, yet we refer to it in our urlpattern as
pages.urls. The reason we do it this way is that that the method
django.urls.include() expects us to pass in a module, or app, as the first argument. So without using
include we would need to import our
pages app, but since we do use
include we don’t have to at the project level!
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) db.sqlite3 helloworld_project/ manage.py pages/ Pipfile Pipfile.lock 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 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. The two most popular choices are Bitbucket and Github.
In this book we will use Bitbucket because it allows private repositories for free. Github charges a fee. Public repositories are available for anyone on the internet to use; private repositories are not. When you’re learning web development, it’s best to stick to private repositories so you don’t inadvertently post critical information such as passwords online.
To get started on Bitbucket, sign up for a free account. After confirming your account via email you’ll be redirected to the Bitbucket welcome page. Click on the link for “Create a repository”.
Then on the “Create Repo” page enter in the name of your repository: “hello-world”. Then click the blue “Create repository button”:
On the next page, click on the link on the bottom for “I have an existing project” which will open a dropdown:
We’re already in the directory for our repo so skip Step 1. In Step 2, we’ll use two commands to add our project to Bitbucket. Note that your command will differ from mine since you have a different username. The general format is the below where
<USER> is your Bitbucket username.
(helloworld) $ git remote add origin https://<USER>@bitbucket.org/<USER>/hello-world.git
After running this command to configure git with this Bitbucket repository, we must “push” our code into it.
(helloworld) $ git push -u origin master
Now if you go back to your Bitbucket page and refresh it, you’ll see the code is now online! Click on the “Source” tab on the left to see it all.
Since we’re done, 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 web server. And we worked with git to track our changes and pushed our code into a private repo on Bitbucket.
Continue on to Chapter 3: Pages app where we’ll build and deploy a more complex Django application using templates and class-based views.