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

    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.

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  2. Skype SMS su Linux: grazie a Skype4Py si puo'!

    Skype
LogoIl client di Skype per Linux non supporta al momento l'invio degli SMS. Questa puo' essere per molti una grossa limitazione, visto che è molto conveniente come metodo per inviare gli sms (costano 10 centesimi) rispetto a molte tariffe in circolazione al momento, con i principali gestori italiani.La mancanza di questa funzionalità è però soltanto apparente! Infatti è stata già implementata a livello di librerie di Skype ed è già disponibile tramite le API.

    Grazie alla libreria Skype4Py, ufficialmente supportata da Skype e sviluppata da Arkadiusz Wahlig (che ha tenuto un talk proprio su questo argomento nella giornata di ieri del PyCon Due), è possibile scrivere applicazioni multipiattaforma (Windows, Linux, Mac) che interagiscano con Skype.

    Una volta installata la libreria nel proprio sistema, dobbiamo soltanto avviare il client Skype.

    Le applicazioni che possiamo scrivere, per automatizzare alcune funzioni di Skype, sono moltissime. In questo caso particolare farò vedere un piccolo script Python che invia un SMS utilizzando il client (ed il credito) dell'istanza di Skype che sta girando sulla vostra macchina:

    [sourcecode language='python']
    import Skype4Py

    number = '+393*********'
    text= 'Messaggio di prova da PySms4Skype!'

    skype = Skype4Py.Skype()
    skype.FriendlyName = 'PySms4Skype'

    skype.Attach()

    sms = skype.CreateSms(Skype4Py.smsMessageTypeOutgoing, number)
    sms.Body = text
    sms.Send()
    [/sourcecode]

    Quando eseguite questo script, Skype vi chiedera' la conferma per autorizzare la vostra applicazione ad utilizzare le API, basterà quindi dare conferma per continuare. Nello script ovviamente dovrete sostituire il numero di telefono con uno valido.

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