Lately I've been interested in improving the interaction of my agilitycourses website for mobile users. One such improvement is to add QR Codes (aka 2D barcodes) representing the page URLs to the printed representations of pages served as PDFs.

I found that developers have reverse engineered the "api" of the goo.gl URL shortening web site. In my brief testing it is very fast. What makes that service extra useful is by adding ".qr" to a shortened URL it returns a PNG image of the QR Code for the shortened URL. That made it perfect for providing both short text and QR Code URL representations for my printed documents.

I threw together a few functions and put them in a module to make it easy to shorten a long URL, obtain the QR Code PNG and store it using Django's Storage functionality:

import osimport urllib
from django.utils import simplejson

def googl_shorten_url(long_url):
    """
    Returns goo.gl shortened url for the provided long_url.
    Code taken from: http://djangosnippets.org/snippets/2220/
    Parameters:
    - `long_url`: the url to supply to goo.gl to be shortened.
    """
    params = urllib.urlencode({'security_token': None, 'url': long_url})
    f = urllib.urlopen('http://goo.gl/api/shorten', params)
    return simplejson.loads(f.read())['short_url']

def googl_qrcode(googl_url):
    """
    Return file containing qr code image file for the given goo.gl url.
    Parameters:
    - `googl_url`: url from which to obtain the qr code.
    """
    return urllib.urlopen(googl_url + '.qr')

def get_url_qr_code_image(long_url, storage, storage_image_file_path=''):
    """
    Return goo.gl shortened url and storage name of qr code corresponding to
    the shortened url for the supplied full url. Contacts goo.gl to shorten
    the supplied long url then downloads and stores the qr code image file
    in the storage instance using the file path and the shortened url name
    as the storage name.
    Parameters:
    - `long_url`: the url to shorten.
    - `storage': a Django storage instance into which to store the qr code
    image.
    - `storage_image_file_path`: file system path to prepend to shortened
    url. This path must exist prior to calling this function.
    """
    try:
        googl_url = googl_shorten_url(long_url)
        qr_file_name = googl_url.split('/')[-1] + '.qr'
        qr_code_name = os.path.join(storage_image_file_path, qr_file_name)
        if not storage.exists(qr_code_name):
            qr_buffer = storage.open(qr_code_name, 'wb')
            qr_buffer.write(googl_qrcode(googl_url).read())
            qr_buffer.close()
    except:
        googl_url = None
        qr_code_name = None
    return googl_url, qr_code_name

Yes, it has a nasty bare try/except. For my uses this is optional functionality so I never want a failure to stop the main functionality of the views that use it. Add exception handling appropriate for your needs.

The main entry point is get_url_qr_code_image(). Here is an example of its use (assuming you save the code in googl.py):

>>> import googl
>>> from django.core.files.storage import default_storage
>>> short_url, qr_code_storage_name = googl.get_url_qr_code_image('http://google.com', default_storage)>>> short_urlu'http://goo.gl/mR2d'
>>> qr_code_storage_nameu'mR2d.qr'
>>> default_storage.path(qr_code_storage_name)u'/home/dev/agilitycourses/static/mR2d.qr'
>>> default_storage.url(qr_code_storage_name)u'mR2d.qr'
>>>

Hope you find this useful.

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