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Python Django media url not working after setting DEBUG = True

As stated in topic, my Django site media url is returning 404 after trying to access it. Everything was working flawless until I wanted to end the development process and set
DEBUG = True
in settings.py to have the site finished once and for all. When I change DEBUG back to
DEBUG = False
it works fine once again. I have no idea what's the problem, any suggestions?

This is by design: https://docs.djangoproject.com/en/dev/howto/static-files/#serving-static-files-during-development
If you use django.contrib.staticfiles as explained above, runserver will do this automatically when DEBUG is set to True.
That being said, you can use the following workaround by modifying your urls.py:
from django.conf import settings
from django.conf.urls.static import static
urlpatterns = patterns('',
# ... the rest of your URLconf goes here ...
) + static(settings.STATIC_URL, document_root=settings.STATIC_ROOT)
+ static(settings.MEDIA_URL, document_root=settings.MEDIA_ROOT)
Note that this is highly inefficient and not encouraged for production use. You should normally configure your web server (apache, nginx, etc) to serve your static and media content.

(Django) How to apply css?

I want to apply CSS on my Django project.
CSS path in my index.html is right but it doesn't work well.
My index.html page show up well in my site,
--app_index
----index.html
----bootstrap
-------css
-----------abc.css
-----------abc2.css
So, must I modify the URL.py file too?

You need to configure static files in your Django app. The following links should help guide you in the right direction:
http://www.tangowithdjango.com/book/chapters/templates_static.html
https://docs.djangoproject.com/en/1.7/howto/static-files/
You will set up your index.html for example in a template directory that can access your static files (e.g. CSS, javascript, static images, etc.) that are located in your static directory.
In response to your question concerning modification of urls.py, the answer is yes. As you will see in the links on configuring static files within your project, you have to add some code to your urls.py. An example of this code might look like this:
if settings.DEBUG:
import debug_toolbar
urlpatterns += patterns(
'django.views.static',
(r'media/(?P<path>.*)',
'serve',
{'document_root': settings.MEDIA_ROOT}),
url(r'^__debug__/', include(debug_toolbar.urls))
)
During development Django serves your static files hence the above code, but during production your static files are served via your configured server (e.g. Apache, nginx).

Django serving dynamic Files

I have a problem about serving admin uploaded files in my templates.
I set:
MEDIA_URL='/media/'
MEDIA_ROOT = 'assets/'
and my models are like:
mainPhoto = models.ImageField(upload_to="articles/")
When in my templates, I try:
<img src="{{MEDIA_URL}}{{article.mainPhoto}}" />
The image doesn't show up on the website.
I found one deprecated solution with the django .serve(), but I hope to avoid using it.
I was looking everywhere and didn't find any answer, so I hope someone here will be able to help me.

There are two parts to make this work. First is the Django configuration. There are really two settings for this which you have already mentioned - MEDIA_URL and MEDIA_ROOT. As already noted in the comments the MEDIA_ROOT has to be an absolute path. For example:
MEDIA_ROOT = `/abs/path/to/project/media/`
Second part is actually serving the files. If you are in production, you NEVER want to serve your static or media files through Django so you should configure Apache or nginx or whatever server system you are using to serve the files instead of Django. If you are on the other hand still developing the app, there is a simple way to make Django serve media files. The idea is to modify your urls.py and use the Django's static files server to serve media files as well:
# urls.py
from django.conf import settings
from django.conf.urls.static import static
urlpatterns = patterns('',
# other patterns
) + static(settings.MEDIA_URL, document_root=settings.MEDIA_ROOT)
More about this approach at Django docs.
Also FYI, you probably should not use {{MEDIA_URL}}{{article.mainPhoto}} to get the url of an image. This approach will break for example if you will no longer use file system storage for static files and will switch to something different like Amazon S3. It is always a good idea for the storage backend to figure out the url:
<img src="{{article.mainPhoto.url}}" />

Django Http404 and DEBUG mode catch 22

I'm using the staticfiles app during development, which doesn't work unless DEBUG is turned on.
From the docs:
Warning This will only work if DEBUG is True.
That's because this view is grossly inefficient and probably insecure.
This is only intended for local development, and should never be used
in production.
Additionally, when using staticfiles_urlpatterns your STATIC_URL
setting can't be empty or a full URL, such as
http://static.example.com/.
I'm trying to view my Http404 templates, though, and of course they don't work in DEBUG mode. So I'm in a catch 22 - if I want to view the 404 page I have to turn off DEBUG, but then no static files are servers and I can't see any images, etc.

You can simply pretend you are in production. Run:
python manage.py collectstatic --noinput
To have all your files copied to STATIC_ROOT. Then, temporarily add the following to urls.py:
urlpatterns += patterns('',
(r'^static/(?P<path>.*)$', 'django.views.static.serve', {'document_root': settings.STATIC_ROOT}),
)
You'll have to run collectstatic each time you make a change to any static files, so I would suggest live-editing in something like Firebug and then saving the finished product. Also, remember to delete the static directory and remove that line from urls.py when you're done.

I haven't tried it myself, but you might try setting DEBUG_PROPAGATE_EXCEPTIONS = True
https://docs.djangoproject.com/en/dev/ref/settings/

Why can't Django find my admin media files once I leave the built-in runserver?

When I was using the built-in simple server, everything is OK, the admin interface is beautiful:
python manage.py runserver
However, when I try to serve my application using a wsgi server with django.core.handlers.wsgi.WSGIHandler, Django seems to forget where the admin media files is, and the admin page is not styled at all:
gunicorn_django
How did this happen?

When I look into the source code of Django, I find out the reason.
Somewhere in the django.core.management.commands.runserver module, a WSGIHandler object is
wrapped inside an AdminMediaHandler.
According to the document, AdminMediaHandler is a
WSGI middleware that intercepts calls
to the admin media directory, as
defined by the ADMIN_MEDIA_PREFIX setting, and serves those images.
Use this ONLY LOCALLY, for development! This hasn't been tested
for
security and is not super efficient.
And that's why the admin media files can only be found automatically when I was using the test server.
Now I just go ahead and set up the admin media url mapping manually :)

Django by default doesn't serve the media files since it usually is better to serve these static files on another server (for performance etc.). So, when deploying your application you have to make sure you setup another server (or virtual server) which serves the media (including the admin media). You can find the admin media in django/contrib/admin/media. You should setup your MEDIA_URL and ADMIN_MEDIA_URL so that they point to the media files. See also http://docs.djangoproject.com/en/dev/howto/static-files/#howto-static-files.

I've run into this problem too (because I do some development against gunicorn), and here's how to remove the admin-media magic and serve admin media like any other media through urls.py:
import os
import django
...
admin_media_url = settings.ADMIN_MEDIA_PREFIX.lstrip('/') + '(?P<path>.*)$'
admin_media_path = os.path.join(django.__path__[0], 'contrib', 'admin', 'media')
urlpatterns = patterns('',
url(r'^admin/', include(admin.site.urls)),
url(r'^' + admin_media_url , 'django.views.static.serve', {
'document_root': admin_media_path,
}, name='admin-media'),
...
)
Also: http://djangosnippets.org/snippets/2547/
And, of course, #include <production_disclaimer.h>.