Thin Django - Guide

gistfile1.py

############ Part 0 - Prerequistes #############
# Step 1 : Setup your virtual environment
# Step 2 : Install the required dependencies
    
    $ pip install django
    $ pip install gunicorn
    $ pip install PIL (For Windows : easy_install PIL)

# Step 3 : Create thin/thin.py

############ Part 1 - Thin Django #############

# Step 1 : Write the basic view

    from django.http.response import HttpResponse

    ## Views
    def home(request):
        return HttpResponse("Hello Django!")

# Step 2 : Add the URL routing

    from django.conf.urls import url

    # Routing
    urlpatterns = (
                   url(r'^$', home, name='home'),
                   )

# Step 3 : Configured the project settings
    
    from django.conf import settings
    
    # Settings
    settings.configure(
                       ROOT_URLCONF = __name__,
                   )

# Step 4 : Configure the entry point and execution
    
    import sys
    from django.core.management import execute_from_command_line

    # Execution
    if __name__ == '__main__':
        execute_from_command_line(sys.argv)

# Step 5 : Run the development server
    
    $ python thin.py runserver

    # It will fail and fix the error by adding DEBUG in the settings

    settings.configure(
                   DEBUG        =   True,
                   ROOT_URLCONF =   __name__,
                   )
    # Run the server again

    $ python thin.py runserver

    # Verify the results in the browser

    http://localhost:8000/

############ Part 1 - Create Thin Django Template #############

# Step 1 : Make it WGSI compatible

    from django.core.wsgi import get_wsgi_application

    application = get_wsgi_application()
    
# Step 2 : [OPTIONAL]Run it with Gunicorn(Works in Linux Only)
    
    $ gunicorn thin.py --log-file=-


# Step 3 : Enhance the DEBUG setting to read it from environment variable

    import os

    DEBUG = os.environ.get('DEBUG', 'on') == 'on',

    # Run the development server and test it

    # Set the DEBUG environment variable to off
        $ set DEBUG=off     # Windows
        $ export DEBUG=off  # Linux

    # Run the development  server and test it
    # Fix the error by adding ALLOWED_HOST settings

    ALLOWED_HOSTS  =  os.environ.get('ALLOWED_HOSTS', 'localhost').split(","),

    # Run the development  server and test it using http://localhost:8000/
    # Run the development  server and test it using http://127.0.0.1:8000/

    # Fix it by setting the ALLOWED_HOSTS environment variable to 127.0.0.1
    
        $ set ALLOWED_HOSTS=127.0.0.1
    
    # Run the development  server and test it using http://127.0.0.1:8000/
    # Run the development  server and test it using http://localhost:8000/
    
    # Fix it by setting the ALLOWED_HOSTS environment variable to 127.0.0.1
    
        $ set ALLOWED_HOSTS=127.0.0.1,localhost
    
    # Unset the DEBUG environment variable
        $ set DEBUG=  # Windows
        $ unset DEBUG   # Linux

    # Run the development  server and test it using http://127.0.0.1:8000/
    # Run the development  server and test it using http://localhost:8000/

# Step 4 : Configure the SECERT_KEY setting to read it from environment variable
    
    SECERT_KEY =   os.environ.get('SECERT_KEY', os.urandom(32)),

# Step 5 : Configure the MIDDLEWARE_CLASSES settings

       MIDDLEWARE_CLASSES = (
                             'django.middleware.common.CommonMiddleware',
                             'django.middleware.csrf.CsrfViewMiddleware',
                             'django.middleware.clickjacking.XFrameOptionsMiddleware',
       ),

# Step 6 : Make this project as a template for startproject

    # Update SECERT_KEY settings

    SECERT_KEY =  os.environ.get('SECERT_KEY', '{{ secert_key }}'),

    # Update home view

    def home(request):
        return HttpResponse("Hello {{ project_name }}!")

    # Copy/Rename the project folder and python module to project_name. It should look like this

    thin/thin.py ==> project_name/project_name.py


############ Part 3 - Sample Project using Thin Django Template - Images with Water Mark #############

# Step 1 : Create a Django project called 'wm_image' from the thin template

    <ENV_PATH>/django-admin.exe startproject wm_image --template=project_name

# Step 2 : Run the development  server and test it
    
    $ python wm_image.py runserver


# Step 3 : Create home page (index.html)

    # Configure the templates directory in settings
    BASE_DIR = os.path.dirname(__file__)

    TEMPLATE_DIRS =  (
                      os.path.join(BASE_DIR, "templates"),
    ),
    
    # Create templates directory and index.html inside it (wm_image/templates/index.html)

    <!DOCTYPE html>
    <html>
        <head>
            <title> Thin Django - Images with Water Mark </title>
        </head>
        <body>
            <h1> Images with Water Mark </h1>
        </body>
    </html>


# Step 4 : Enhance the home page view

    from django.shortcuts import render

    def home(request):
        return render(request, "index.html")

    # Run the development server and test it

# Step 5 : Define the URL Routing for water mark images
    
    # Routing
    urlpatterns = (
                   url(r'^image/(?P<image_url>.*)/(?P<water_mark_text>.*)/$', water_mark_image, name='water_mark_image'),
                   url(r'^$', home, name='home'),
    )


# Step 6 : Create dummy 'water_mark_image' view

    def water_mark_image(request, image_url, water_mark_text):
        return HttpResponse("<Image>")

# Step 7 : Enhance the <body> of index.html to render the images with water mark

    <img src=" {% url 'water_mark_image' water_mark_text='Company ABC' image_url='<Image URL>' %} "/>
    <img src=" {% url 'water_mark_image' water_mark_text='Company ABC' image_url='http://static.guim.co.uk/sys-images/Guardian/Pix/pictures/2013/1/9/1357751342331/DJANGO-UNCHAINED-008.jpg' %} "/>

    # Run the development server and test it

# Step 8 : Implement ImageForm to handle the validations

    from django import forms

    ## Forms
    class ImageForm(forms.Form):
        image_url           =   forms.URLField()
        water_mark_text     =   forms.CharField(min_length=3)


# Step 9 : Use the form inside the 'water_mark_image' view

    def water_mark_image(request, image_url, water_mark_text):
        image_form = ImageForm({'image_url'         : image_url,
                                'water_mark_text'   : water_mark_text
                                })

        if image_form.is_valid() is False:
            return HttpResponseBadRequest("Invalid Data Supplied.")

        return HttpResponse("<Image>")

# Step 10 : Test the form validations using some invalid data for image_url and water_mark_text

    <img src=" {% url 'water_mark_image' water_mark_text='Company ABC' image_url='dummy' %} "/>
    <img src=" {% url 'water_mark_image' water_mark_text='BC' image_url='http://static.guim.co.uk/sys-images/Guardian/Pix/pictures/2013/1/9/1357751342331/DJANGO-UNCHAINED-008.jpg' %} "/>

# Step 11 : Add a method to generate the water marker image in ImageForm

    def add_water_mark(self):
        image_url           =   self.cleaned_data['image_url']
        water_mark_text     =   self.cleaned_data['water_mark_text']

# Step 12 : Enhance the 'water_mark_image' view to use 'add_water_mark' method from ImageForm

    if image_form.is_valid() is False:
        return HttpResponseBadRequest("Invalid Data Supplied.")

    image = image_form.add_water_mark()
    return HttpResponse(image, content_type='image/png')

# Step 13 : Download and save the given Image URL in the 'add_water_mark'

    # Create images folder to save the downloaded images (wm_image/images)

    import urllib
    import hashlib

    # Download the image from image_url
    image_key      = hashlib.sha224(image_url).hexdigest()
    image_location = os.path.join('images', image_key)

    with open(image_location, 'wb') as fp:
        fp.write(urllib.urlopen(image_url).read())

# Step 14 : Write the given water mark text on the image
    
    # easy_install pil (Windows) or pip install pil (Linux)

    from _io import BytesIO
    
    import Image
    import ImageDraw

    image_content = Image.open(image_location)
    draw = ImageDraw.Draw(image_content)

    draw.text((100, 100), water_mark_text, (255, 0 , 0))

    content = BytesIO()
    image_content.save(content, "PNG")
    content.seek(0)

    return content

    # Run the development server and test it

# Step 15 : Add few more water marked images (same image with different text)

    <img src=" {% url 'water_mark_image' water_mark_text='Company MNO' image_url='http://static.guim.co.uk/sys-images/Guardian/Pix/pictures/2013/1/9/1357751342331/DJANGO-UNCHAINED-008.jpg' %} "/>
    <img src=" {% url 'water_mark_image' water_mark_text='Company XYZ' image_url='http://static.guim.co.uk/sys-images/Guardian/Pix/pictures/2013/1/9/1357751342331/DJANGO-UNCHAINED-008.jpg' %} "/>

    # Run the development server and test it

# Step 16 : Use cache to avoid duplicate downloads

    from django.core.cache import cache
    
    # Download the image from image_url
    image_key      = hashlib.sha224(image_url).hexdigest()

    # Check in cache
    image_location = cache.get(image_key)

    if image_location is None:
        print "Not found in Cache", water_mark_text, image_url
        image_location = os.path.join('images', image_key)

        with open(image_location, 'wb') as fp:
            fp.write(urllib.urlopen(image_url).read())

        cache.set(image_key, image_location)
    else :
        print "Found in Cache", water_mark_text, image_url
    
    # Run the development server and fix the error by 
        # Moving the settings to the top
        # Import the cache after settings

        # Settings
        BASE_DIR = os.path.dirname(__file__)
        settings.configure(
                           DEBUG            =   os.environ.get('DEBUG', 'on') == 'on',
                           ALLOWED_HOSTS    =   os.environ.get('ALLOWED_HOSTS', 'localhost').split(","),
                           SECERT_KEY       =   os.environ.get('SECERT_KEY', ''),
                           ROOT_URLCONF     =   __name__,

                           MIDDLEWARE_CLASSES   = (
                                                   'django.middleware.common.CommonMiddleware',
                                                   'django.middleware.csrf.CsrfViewMiddleware',
                                                   'django.middleware.clickjacking.XFrameOptionsMiddleware',
                           ),
                           TEMPLATE_DIRS        =  (
                                                    os.path.join(BASE_DIR, "templates"),
                           ),
        )

        from django.core.cache import cache

        ## Forms
        class ImageForm(forms.Form):

    # Run the development server and test it

# Step 17 : Implement ETAGs to cache in the middleware level

    from django.views.decorators.http import etag

    def etag_water_mark_image(request, image_url, water_mark_text):
        wm_key = "WM : {} : {}".format(image_url, water_mark_text)
        return hashlib.sha224(wm_key.encode('utf-8')).hexdigest()

    @etag(etag_water_mark_image)
    def water_mark_image(request, image_url, water_mark_text):
        print "ETAG NOT HIT", water_mark_text, image_url

    # Remove the print statements from ImageForm
    # Run the development server and test it

# Step 18 : Add different images and test the etag and cache content