Q:

Django: custom middleware called twice

I have a custom middleware which is called twice for every request and I don't understand why. 
This is my middleware:
class MyMiddleWare(object):

  def process_request(self, request):
    print 'FOO'
    return None

This is my middleware setting:
MIDDLEWARE_CLASSES = (
    'django.middleware.common. CommonMiddleware',
    'django.contrib.sessions.middleware. SessionMiddleware',
    'django.middleware.locale. LocaleMiddleware',
    'django.middleware.csrf. CsrfViewMiddleware',
    'django.contrib.auth.middleware. AuthenticationMiddleware',
    'django.contrib.messages.middleware. MessageMiddleware',
    'MyMiddleware',
)

And this is the output in the console after homepage request: 
[28/Jun/2013 19:48:26] FOO
[28/Jun/2013 19:48:26] "GET / HTTP/1.1" 200 7468
[28/Jun/2013 19:48:27] FOO

I tried to comment out all the other middlewares and the problem is the same.  What should I do? 
ps: the described behavior is replicable in each view
UPDATE:
I tried to implement process_view rather than process_request and it is called once as expected... why? 
UPDATE 2:
process_response is called twice like process_request
UDATE 3:
ooooh shiiiit!  It's a request to favicon.ico (which I haven't defined myself)... who is calling this file? 

A:

The problem is that if you serve favicon.ico by defining it as django url (like the code below):
(r'^favicon\.ico$',
  'django.views.generic.simple.redirect_to',
  {'url': settings. MEDIA_URL+'images/favicon.ico'}),

All your middleware get called twice: 1 time for the page you have requested + 1 time for the favicon (which is always called by the browser). 
The solution is simple: don't use django urls to serve your vaficon, instead put something like:
<link rel="icon" type="image/png" href="{% static 'core/img/favicon.ico' %}" />

in the <head> of your base template!