Creating a production ready API with Python and Django Rest Framework - part 1

Posted on Wed 28 September 2016 in Development • Tagged with API, Django, framework, Python, rest, tutorial

The aim if this tutorial is to show how to create a production ready solution for a REST API, using Python and Django Rest Framework. I will show you how to first create a very basic API, how to handle the authentication and permissions and I will cover deployment and hosting of images. The full source code of the tutorial is available at: https://github.com/andreagrandi/drf-tutorial

Summary of the complete tutorial

  1. Create the basic structure for the API
  2. Add Authentication and POST methods
  3. Handling details and changes to existing data
  4. Testing the API
  5. Switching from Sqlite to PostgreSQL
  6. Hosting the API on Heroku
  7. Add an Image field and save images to S3

Create the basic structure for the API

For this tutorial I will assume you have correctly installed at least Python (I will use Python 2.7.x), virtualenv and virtualenvwrapper on your system and I will explain how to create everything else step by step.

Note: at the time of writing, the tutorial has been based on Django 1.10.1 and Django Rest Framework 3.4.7

Creating the main project structure

mkdir drf-tutorial
mkvirtualenv drf-tutorial
cd drf-tutorial
pip install django djangorestframework
django-admin.py startproject drftutorial .
cd drftutorial
django-admin.py startapp catalog

Data Model

We will create the API for a generic products catalog, using a very simple structure (to keep things simple). Edit the file catalog/models.py adding these lines:

from __future__ import unicode_literals
from django.db import models


class Product(models.Model):
    name = models.CharField(max_length=255)
    description = models.TextField()
    price = models.DecimalField(decimal_places=2, max_digits=20)

after creating the model, we need to add 'catalog' application to INSTALLED_APPS. Edit settings.py and add the app at the end of the list:

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'catalog',
]

at this point the Django application will be recognised by the project and we can create and apply the schema migration:

(drf-tutorial) ➜  drftutorial git:(235dfcc) ✗ ./manage.py makemigrations
Migrations for 'catalog':
    catalog/migrations/0001_initial.py:
        - Create model Product

(drf-tutorial) ➜  drftutorial git:(235dfcc) ✗ ./manage.py migrate
Operations to perform:
    Apply all migrations: admin, auth, catalog, 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 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 catalog.0001_initial... OK
        Applying sessions.0001_initial... OK

API Serializer

Serializers are those components used to convert the received data from JSON format to the relative Django model and viceversa. Create the new file catalog/serializers.py and place this code inside:

from .models import Product
from rest_framework import serializers


class ProductSerializer(serializers.ModelSerializer):
    class Meta:
        model = Product
        fields = ('name', 'description', 'price')

In this case we are using a ModelSerializer. We need to create a new class from it, and specify the model attribute, that's it. In this case we also specify the fields we want to return.

API View

The serializer alone is not able to respond to an API request, that's why we need to implement a view. In this first version of the view (that we will improve soon) we will "manually" transform the data available in the serializer dictionary to a JSON response. In catalog/views.py add this code:

from django.http import HttpResponse
from rest_framework.renderers import JSONRenderer
from rest_framework.parsers import JSONParser
from .models import Product
from .serializers import ProductSerializer


class JSONResponse(HttpResponse):
    """
    An HttpResponse that renders its content into JSON.
    """
    def __init__(self, data, **kwargs):
        content = JSONRenderer().render(data)
        kwargs['content_type'] = 'application/json'
        super(JSONResponse, self).__init__(content, **kwargs)


def product_list(request):
    if request.method == 'GET':
        products = Product.objects.all()
        serializer = ProductSerializer(products, many=True)
        return JSONResponse(serializer.data)

At this point we need to tell our Django app to use this API view when a certain URL is requested. We first need to add this code in catalog/urls.py

from django.conf.urls import url
from . import views

urlpatterns = [
    url(r'^products/$', views.product_list),
]

and finally we need to add this to drftutorial/urls.py

from django.conf.urls import url, include
from django.contrib import admin

urlpatterns = [
    url(r'^admin/', admin.site.urls),
    url(r'^', include('catalog.urls')),
]

Testing our work

At this point we should be able to start our Django app:

./manage.py runserver

Let's install a tool that will help us to test the API:

pip install httpie

now we can use it to call our URL:

$ http http://127.0.0.1:8000/products/
HTTP/1.0 200 OK
Content-Type: application/json
Date: Wed, 28 Sep 2016 09:54:50 GMT
Server: WSGIServer/0.1 Python/2.7.11
X-Frame-Options: SAMEORIGIN

[]

It works! It's an empty response of course, because we still don't have any data to show, but we will see later how to load some example data in our database. If you have been able to follow the tutorial up to this point, that's good. If not, don't worry. You can checkout the code at exactly this point of the tutorial doing:

git checkout tutorial-1.0

Improving the API View

There is a quicker and more efficient way of implementing the same API view we have seen before. We can use a class based view, in particular the APIView class and also have the JSON response implemented automatically. Change the code inside catalog/views.py with this one:

from django.http import HttpResponse
from rest_framework.views import APIView
from rest_framework.response import Response
from .models import Product
from .serializers import ProductSerializer


class ProductList(APIView):
    def get(self, request, format=None):
        products = Product.objects.all()
        serializer = ProductSerializer(products, many=True)
        return Response(serializer.data)

You will also have to change catalog/urls.py in this way:

urlpatterns = [
    url(r'^products/$', views.ProductList.as_view()),
]

You can check the source code for this step of the tutorial with:

git checkout tutorial-1.1

There is also another way of writing the same view. Let's try it with ListAPIView. Edit catalog/views.py again and substitute the code with this one:

from django.http import HttpResponse
from rest_framework import generics
from rest_framework.response import Response
from .models import Product
from .serializers import ProductSerializer


class ProductList(generics.ListAPIView):
    queryset = Product.objects.all()
    serializer_class = ProductSerializer

With a ListAPIView we are basically creating a read-only API that is supposed to return a list of items. We need to specify a queryset and the serializer_class parameters. Once again, you can get up to this point, checking out the related git tag:

git checkout tutorial-1.2

Creating Initial Data

An API that doesn't return any data is not very useful, right? Also, at the moment we haven't implemented yet any feature that let us insert any data. That's why I've created a data migration for you that will insert some data for you. You may notice that the example data contains some Italian products... out of the scope of this tutorial, I strongly advise you to google this products and if you ever happen to visit Italy, try them. You won't regret!

Going back to our data migration, you first have to create an empty one with:

./manage.py makemigrations --empty catalog

and then open the file that has been created under catalog/migrations/ named 0002_..... (your name will be different from mine, so just edit the one starting with 0002 and you will be fine) and fill it with this code:

from __future__ import unicode_literals
from django.db import migrations


def create_initial_products(apps, schema_editor):
    Product = apps.get_model('catalog', 'Product')

    Product(name='Salame', description='Salame Toscano', price=12).save()
    Product(name='Olio Balsamico', description='Olio balsamico di Modena', price=10).save()
    Product(name='Parmigiano', description='Parmigiano Reggiano', price=8.50).save()
    Product(name='Olio', description='Olio Oliva Toscano', price=13).save()
    Product(name='Porchetta', description='Porchetta toscana cotta a legna', price=7.50).save()
    Product(name='Cantucci', description='Cantucci di Prato', price=4).save()
    Product(name='Vino Rosso', description='Vino Rosso del Chianti', price=9.50).save()
    Product(name='Brigidini', description='Brigidini di Lamporecchio', price=3.50).save()


class Migration(migrations.Migration):

    dependencies = [
        ('catalog', '0001_initial'),
    ]

    operations = [
        migrations.RunPython(create_initial_products),
    ]

to apply the migration we just created, just do:

./manage.py migrate

If you try to test the API again from the command line, you will get these products back:

$ http http://127.0.0.1:8000/products/
HTTP/1.0 200 OK
Allow: GET, HEAD, OPTIONS
Content-Type: application/json
Date: Wed, 28 Sep 2016 12:29:36 GMT
Server: WSGIServer/0.1 Python/2.7.11
Vary: Accept, Cookie
X-Frame-Options: SAMEORIGIN

[
    {
        "description": "Salame Toscano",
        "name": "Salame",
        "price": "12.00"
    },
    {
        "description": "Olio balsamico di Modena",
        "name": "Olio Balsamico",
        "price": "10.00"
    },
    {
        "description": "Parmigiano Reggiano",
        "name": "Parmigiano",
        "price": "8.50"
    },
    {
        "description": "Olio Oliva Toscano",
        "name": "Olio",
        "price": "13.00"
    },
    {
        "description": "Porchetta toscana cotta a legna",
        "name": "Porchetta",
        "price": "7.50"
    },
    {
        "description": "Cantucci di Prato",
        "name": "Cantucci",
        "price": "4.00"
    },
    {
        "description": "Vino Rosso del Chianti",
        "name": "Vino Rosso",
        "price": "9.50"
    },
    {
        "description": "Brigidini di Lamporecchio",
        "name": "Brigidini",
        "price": "3.50"
    }
]

Again, you can get up to this point with:

git checkout tutorial-1.3

One more thing...

No, we are not going to present a new amazing device, I'm sorry, but I want to show you a nice Django Rest Framework feature you can have without much additional work. Edit settings.py and add rest_framework to the list of INSTALLED_APPS:

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'rest_framework',
    'catalog',
]

Now, if you are still running the Django app, try to visit this url from your browser: http://127.0.0.1:8000/products/
That's very nice, isn't it? You can have browsable APIs at no cost.

Wrapping Up

I've mentioned at the beginning that this is just the first part of my API tutorial. In the next part I will show you how to let the consumer of your API add some products and leave reviews (we will introduce a new model for this). Also, we will see how to set proper permissions to these new API methods so that only admin users will be able to add products while normal users will be able to add reviews. So, if you feel ready, you can begin to follow the second part of this tutorial

References

Some parts of this tutorial and a few examples have been taken directly from the original Django Rest Framework tutorial.


How to write a custom Django Middleware

Posted on Sun 23 August 2015 in Development • Tagged with Django, HowTo, middleware, Python, tutorial

To understand how a Django Middleware works we need to remember that the basic architecture of Django is composed by a request and a response. A middleware is something that stays in the middle. Let's give a look to the next diagram, taken from official Django documentation:

middleware

Important things to know

There are four important things to know about middlewares:

  • You need to write a class that just inherit from object
  • The order where you place your middleware in settings.py is important: middlewares are processed from top to bottom during a request and from bottom to top during a response.
  • You don't need to implement all the available methods of a middleware. For example you can just implement process_request and process_template_response
  • If you implement process_request and you decide to return an HttpResponse, all the other middlewares, views etc... will be ignored and only your response will be returned

Writing a middleware

In my example I wanted to implement a feature that saves the time when a request is made and the time when a request has been processed, then calculates the time delta and exposes this value in the context so that is accessible from our templates. How to implement a similar feature using a middleware? Here is my example:

from datetime import datetime


class BenchmarkMiddleware(object):
    def process_request(self, request):
        request._request_time = datetime.now()

    def process_template_response(self, request, response):
        response_time = request._request_time - datetime.now()
        response.context_data['response_time'] = abs(response_time)
        return response

Please don't care about how I calculated the time. I'm aware that there are better ways to do it, but I just wanted to keep it simple and show how to implement a simple middleware.

If you want to see a complete example of a project that includes and uses this middleware, here you can find the complete source code: https://github.com/andreagrandi/benchmark-middleware-example

References


Using GtkIconView in Python: a small tutorial

Posted on Tue 15 April 2008 in Linux, Programmazione, Python • Tagged with gtk, gtkiconview, gtkliststore, HowTo, programming, Python, tutorial

In these days I was looking for a simple tutorial to understand how to use GtkIconView, but the only thing I was able to find was an example in PHP-Gtk. So I decided to translate it in Python language, thinking it would be useful for other people trying to use that Gtk control. You can find the code here:

import gtk
import gobject

DEFAULT_IMAGE_WIDTH = 100

# Main Window setup  
window = gtk.Window(gtk.WINDOW_TOPLEVEL)
window.set_size_request(400, 240)
window.connect("destroy", gtk.main_quit)
window.set_title("Python GtkIconView Test")

# Add a VBox  
vbox = gtk.VBox()  
window.add(vbox)

# Setup Scrolled Window  
scrolled_win = gtk.ScrolledWindow()
scrolled_win.set_policy(gtk.POLICY_AUTOMATIC, gtk.POLICY_AUTOMATIC)

# Setup ListStore to contain images and description  
model = gtk.ListStore(gtk.gdk.Pixbuf, gobject.TYPE_STRING)

# Create a tuple with image files
immagini = (
    "BD786-TFR.jpg", "guido_sottozero.jpg", "IMG_0056.JPG", "movies_card.jpg"
)

for im in immagini:
    try:  
        pixbuf = gtk.gdk.pixbuf_new_from_file(im)
        pix_w = pixbuf.get_width()
        pix_h = pixbuf.get_height()
        new_h = (pix_h * DEFAULT_IMAGE_WIDTH) / pix_w # Calculate the scaled height before resizing image
        scaled_pix = pixbuf.scale_simple(
            DEFAULT_IMAGE_WIDTH, new_h, gtk.gdk.INTERP_TILES
        )
        model.append((scaled_pix, im))
    except:
        pass

# Setup GtkIconView  
view = gtk.IconView(model)  # Pass the model stored in a ListStore to the GtkIconView
view.set_pixbuf_column(0)
view.set_text_column(1)
view.set_selection_mode(gtk.SELECTION_MULTIPLE)
view.set_columns(0)
view.set_item_width(150)

# Pack objects and show them all  
scrolled_win.add(view)  
vbox.pack_start(scrolled_win)
window.show_all()

gtk.main()

The important thing to notice is that you have to store all the images in a GtkListStore and pass it to the GtkIconView as "model" parameter. I hope this example is clear. If you have any question, please comment this post and I'll try to answer.

This is a screenshot of this example:

gtkiconview