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creating a new instance of todolist in every URL [duplicate]

I've googled around for this, but I still have trouble relating to what Django defines as "apps".
Should I create a new app for each piece of functionality in a site, even though it uses models from the main project?
Do you guys have good rule of thumb of when to split off a new app, and when to keep functionality together with the "main project" or other apps?

James Bennett has a wonderful set of slides on how to organize reusable apps in Django.

I prefer to think of Django applications as reusable modules or components than as "applications".
This helps me encapsulate and decouple certain features from one another, improving re-usability should I decide to share a particular "app" with the community at large, and maintainability.
My general approach is to bucket up specific features or feature sets into "apps" as though I were going to release them publicly. The hard part here is figuring out how big each bucket is.
A good trick I use is to imagine how my apps would be used if they were released publicly. This often encourages me to shrink the buckets and more clearly define its "purpose".

Here is the updated presentation on 6 September 2008.
DjangoCon 2008: Reusable Apps #7:53
Slide: Reusable_apps.pdf
Taken from the slide
Should this be its own application?
Is it completely unrelated to the app’s focus?
Is it orthogonal to whatever else I’m doing?
Will I need similar functionality on other sites?
If any of them is "Yes"? Then best to break it into a
separate application.

I tend to create new applications for each logically separate set of models. e.g.:
User Profiles
Forum Posts
Blog posts

The two best answers to this question I've found around the web are:
The Reusable Apps Talk (slides)(video) also mentioned in other answers. Bennett, the author and Django contributor, regularly publishes apps for others to use and has a strong viewpoint towards many small apps.
Doordash's Tips for Django at Scale which gives the opposite advice and says in their case they migrated to one single app after starting with many separate apps. They ran into problems with the migration dependency graph between apps.
Both sources agree that you should create a separate app in the following situations:
If you plan to reuse your app in another Django project (especially if you plan to publish it for others to reuse).
If the app has few or no dependencies between it and another app. Here you might be able to imagine an app running as its own microservice in the future.

The rule I follow is it should be a new app if I want to reuse the functionality in a different project.
If it needs deep understanding of the models in your project, it's probably more cohesive to stick it with the models.

The best answer to this question is given by Andrew Godwin (Django core developer):
The main purpose of apps is, in my eyes, to provide logical separation of reusable components - specifically, a first-class namespace for models/admin/etc. - and to provide an easy way to turn things “on” or “off”.
In some ways, it’s a relic of the time when Django was created - when Python packaging and modules were much less developed and you basically had to have your own solution to the problem. That said, it’s still a core part of Django’s mental model, and I think INSTALLED_APPS is still a cleaner, easier solution than Python’s replacement offering of entrypoints (which makes it quite hard to disable a package that is installed in an environment but which you don’t want to use).
Is there anything specifically you think could be decoupled from the app concept today? Models and admin need it for autodiscovery and a unique namespace prefix, so that’s hard to undo, and I’m struggling to think of other features you need it for (in fact, if all you want is just a library, you can make it a normal Python one - no need for the app wrapping unless you’re shipping models, templates or admin code IIRC)

An 'app' could be many different things, it all really comes down to taste. For example, let's say you are building a blog. Your app could be the entire blog, or you could have an 'admin' app, a 'site' app for all of the public views, an 'rss' app, a 'services' app so developers can interface with the blog in their own ways, etc.
I personally would make the blog itself the app, and break out the functionality within it. The blog could then be reused rather easily in other websites.
The nice thing about Django is that it will recognize any models.py file within any level of your directory tree as a file containing Django models. So breaking your functionality out into smaller 'sub apps' within an 'app' itself won't make anything more difficult.

where to put non-model classes in django

I'm now using django 1.6
As I know, if I want to use some model classes (using ORM) I should put them under folder myapp/models.py.
So what if I want to write some non-model classes (not using ORM), i.e. class Util, and only contains some globally used methods, maybe date formatting or something else.
So, where should these code locate? Is there a generally used way to this case?

You can really put them anywhere you like, but I follow the pattern Django itself uses (in admin, cache, etc.) and put such things in a utils.py file. I have one (if necessary) in each app folder, as well as one for the whole project.

Hyphen in django app

Well I stumbled upon a problem with imports and a Django app that has a hyphen in its name.
As far as I know hyphens aren't even allowed in Django app names but it's still there and the website runs without errors. I have absoltuely no idea of how the app was created since the project already existed when I started working on it. (It's a Django CMS project if that changes anything btw)
Now the problem is that when I want to import something in the shell or in a project I can't just write from my-app import module since it always throws an error because of the hypen.
Also in the INSTALLED_APPS it is listed with the hypen INSTALLED_APPS = ('my-app')
So how can I actually fix this and make it useable? I thought about renaming but I don't really know the consequences and I also don't really want to break anything in the CMS (I'm still learning Django and the CMS is very new to me)

You can do this:
import importlib
module = importlib.import_module('.module', 'my-app')
See documentation for more info https://docs.python.org/3/library/importlib.html#importlib.import_module
Edit: This is not a Django specific issue, it is that in Python (and in most other programming languages) '-' (hyphen) can't be used in variable names (As '-' is the subtraction operator).

What is a good Django workflow?

I'm a beginner to Python and Django.
When starting a new project what do you do first before diving into the code?
For example, one could take the following steps:
Configure the settings.py file first
Configure models.py to lay out data structure
Create template files
Define the views/pages
Syncdb
etc
So my question is, what is a good workflow to get through the required steps for a Django application? This also serves as a checklist of things to do. In the definitive guide to Django, the author talks about approaching top down or bottom up. Can anyone expand further on this and perhaps share their process?
Thanks.

Follow the Agile approach. Finish one small case, from the start to the end. From the models to the tests to user experience. Then build on it. Iterate.
Thats the right way to software development.
To do it efficiently, you need: (don't bother right away, you will need it.)
Automated schema migration, automated build system, auto updating and deployment. - None of these, django has got anything to do with. Use pip, fabric, hudson, twill and south appropriately.
Take care not to over burden yourself with all these right away, particularly since you say, you are beginning.

the required steps for a Django application?
There are two required steps.
Write the settings. Write the urls.py
The rest of the steps are optional.
This also serves as a checklist of things to do.
Bad policy. You don't need a checklist of Django features. You need a collection of use cases or user stories which you must implement.
For some reason, you've omitted the two most important and valuable features of Django. Configure the default admin interface and write unit tests. The default admin interface is very high value. Unit testing is absolutely central.
You do it like this.
Gather use cases.
Prioritize the use cases.
Define the actors. The classes of actors becomes groups in the security model.
Define enough "applications" to satisfy the first release of use cases. Define the url structure. Cool URL's don't change.
Build the first use case: models (including security), admin, urls, tests, forms, views and templates. Note that these are the file names (models.py, admin.py, ...) except for templates. Also note that forms and admin should be defined in separate modules even though this isn't required. Also note that templates will be split between a generic templates directory for top-level stuff and application-specific templates.
Build the second use case: models (including security), admin, urls, tests, forms, views and templates.
...
n. Package for release. Tweak up the settings. Configure database and mod-wsgi

I personally can't make a template without writing the views (unless it's a photoshop draft) but in general that's the way I go after I have a plan.
What's extremely important for me is that I don't dive head-first into the code, and that I spend time mocking up the model structure based on the "screens" or "pages" that the user will see.
Once I have a user experience defined, I make sure the backend is robust enough to handle that experience. If I don't visualize the user experience, details get left out that are certainly accomplishable in the shell but not ideal for the website, default django admin, etc.
There are always tradeoffs between agile development and a huge spec: I think there's an important balance. Agile is good: there's no point planning every detail before writing your first line of code, as your needs will change by the time you get to the end. You don't know how your users will really use the site.
On the other hand, without a plan, you can end up with a messy foundation that affects all future code.
An educated guess is a good start. Don't think or assume too much, but definitely have a clear idea how your users will interact with your site for stage 1.

Always try to remember about a DRY rule. For example, why to write RequestContext every new view is defined, where you can simply write a function once, which will add it for you. Good description is here in another topic.
Try to keep a code written one way. Each time you upgrade a schema of your view, edit it in all already written views. That will help keep your code clear and save a lot time for you in future.
Generally good rule, and how do I write my applications is the rule of small steps. Start with writing a settings and urls, then add one model and one view. When it works, modify - add another models or another views. You won't even notice, when your project becomes bigger and bigger.
And the last useful rule for clarity of all the source. Keep files in folders. If you have two subsites based one one (for example "accounts" and "blogs") create two directories names the same. Remeber to put init.py file in each directory. It's really easy to forget. With this practice it's easy to write models and views dedicated to each category. By the way it's a good practice to keep urls like in a tree structure. Main urls.py should contain only links like this one:
(r'^accounts/', include('your_main_name.accounts.urls')),
and of course all media, static, css and so on. In accounts directory urls keep:
urlpatterns = patterns('your_main_name.accounts.views',
url(r'^$', 'index', name='index'),
)
with all views subdirectories.
Last one - keep code clear with actuall django version. Remeber, that the 3.0 release is comming soon.
Hope this will help.

I find that my process varies depending on a lot of variables, mainly whether I know something will work or if I'm experimenting and also whether I'm developing on my production server or in a development environment.
For example, I often do my development directly on the deployment server (most of my work is for intranet projects so there isn't any security risk, etc). But when I do this I really need to make sure the settings and urls are setup first and that gunicorn and nginx are configured.
If I know something should work, or am setting up a generic base set of code, sometimes I'll do all that coding for views and models before I even get enough setup to even run the development server. But when experimenting with new code I find it's good to be able to test every step of the way, so in that case you need your servers running.
In general I do settings, models, syncdb, views, urls, templates, collectstatic, graphics/aesthetics
In general I leave my base.html very plain until the everything else is working, then I add css/js etc.
I guess my point here is that there isn't really a wrong answer for how you do it, and there isn't even only one best practice (as far as I'm concerned). When you do more work, you'll find what you are comfortable with and it'll even vary from project to project.
Good luck, hopefully you learn to love django!

here is something I do in general,
configure basic settings
configure root url.py
configure settings, url.py for static (media) files
create model
sync db
write views (use simple template, if needed)
once you are done with back end implementation
think about UI
prepare styles, scripts
start working on template implementation

Django: "projects" vs "apps"

I have a fairly complex "product" I'm getting ready to build using Django. I'm going to avoid using the terms "project" and "application" in this context, because I'm not clear on their specific meaning in Django.
Projects can have many apps. Apps can be shared among many projects. Fine.
I'm not reinventing the blog or forum - I don't see any portion of my product being reusable in any context. Intuitively, I would call this one "application." Do I then do all my work in a single "app" folder?
If so... in terms of Django's project.app namespace, my inclination is to use myproduct.myproduct, but of course this isn't allowed (but the application I'm building is my project, and my project is an application!). I'm therefore lead to believe that perhaps I'm supposed to approach Django by building one app per "significant" model, but I don't know where to draw the boundaries in my schema to separate it into apps - I have a lot of models with relatively complex relationships.
I'm hoping there's a common solution to this...

Once you graduate from using startproject and startapp, there's nothing to stop you from combining a "project" and "app" in the same Python package. A project is really nothing more than a settings module, and an app is really nothing more than a models module—everything else is optional.
For small sites, it's entirely reasonable to have something like:
site/
models.py
settings.py
tests.py
urls.py
views.py

Try to answer question: "What does my
application do?". If you cannot answer
in a single sentence, then maybe you can
split it into several apps with cleaner
logic.
I read this thought somewhere soon after I've started to work with django and I find that I ask this question of myself quite often and it helps me.
Your apps don't have to be reusable, they can depend on each other, but they should do one thing.

What is to stop you using myproduct.myproduct? What you need to achieve that roughly consists of doing this:
django-admin.py startproject myproduct
cd myproduct
mkdir myproduct
touch myproduct/__init__.py
touch myproduct/models.py
touch myproduct/views.py
and so on. Would it help if I said views.py doesn't have to be called views.py? Provided you can name, on the python path, a function (usually package.package.views.function_name) it will get handled. Simple as that. All this "project"/"app" stuff is just python packages.
Now, how are you supposed to do it? Or rather, how might I do it? Well, if you create a significant piece of reusable functionality, like say a markup editor, that's when you create a "top level app" which might contain widgets.py, fields.py, context_processors.py etc - all things you might want to import.
Similarly, if you can create something like a blog in a format that is pretty generic across installs, you can wrap it up in an app, with its own template, static content folder etc, and configure an instance of a django project to use that app's content.
There are no hard and fast rules saying you must do this, but it is one of the goals of the framework. The fact that everything, templates included, allows you to include from some common base means your blog should fit snugly into any other setup, simply by looking after its own part.
However, to address your actual concern, yes, nothing says you can't work with the top level project folder. That's what apps do and you can do it if you really want to. I tend not to, however, for several reasons:
Django's default setup doesn't do it.
Often, I want to create a main app, so I create one, usually called website. However, at a later date I might want to develop original functionality just for this site. With a view to making it removable (whether or not I ever do) I tend to then create a separate directory. This also means I can drop said functionality just by unlinking that package from the config and removing the folder, rather than a complex delete the right urls from a global urls.py folder.
Very often, even when I want to make something independent, it needs somewhere to live whilst I look after it / make it independent. Basically the above case, but for stuff I do intend to make generic.
My top level folder often contains a few other things, including but not limited to wsgi scripts, sql scripts etc.
django's management extensions rely on subdirectories. So it makes sense to name packages appropriately.
In short, the reason there is a convention is the same as any other convention - it helps when it comes to others working with your project. If I see fields.py I immediately expect code in it to subclass django's field, whereas if I see inputtypes.py I might not be so clear on what that means without looking at it.

I've found the following blog posts very useful about django applications and projects:
http://www.b-list.org/weblog/2006/sep/10/django-tips-laying-out-application/
http://web.archive.org/web/20080302205555/www.pointy-stick.com/blog/2007/11/09/django-tip-developing-without-projects/
In principle, you have a lot of freedom with django for organizing the source code of your product.

If so... in terms of Django's project.app namespace, my inclination is to usemyproduct.myproduct, but of course this isn't allowed
There is nothing like not allowed. Its your project, no one is restricting you. It is advisable to keep a reasonable name.
I don't see any portion of my product being reusable in any context. Intuitively, I would call this one "application." Do I then do all my work in a single "app" folder?
In a general django project there are many apps (contrib apps) which are used really in every project.
Let us say that your project does only one task and has only a single app (I name it main as thethe project revolves around it and is hardly pluggable). This project too still uses some other apps generally.
Now if you say that your project is using just the one app (INSTALLED_APPS='myproduct') so what is use of project defining the project as project.app, I think you should consider some points:
There are many other things that the code other than the app in a project handles (base static files, base templates, settings....i.e. provides the base).
In the general project.app approach django automatically defines sql schema from models.
Your project would be much easier to be built with the conventional approach.
You may define some different names for urls, views and other files as you wish, but I don't see the need.
You might need to add some applications in future which would be real easy with the conventional django projects which otherwise it may become equally or more difficult and tedious to do.
As far as most of the work being done in the app is concerned, I think that is the case with most of django projects.

Here Django creators points out that difference themselves.
I think that thinking about Apps as they have to be reusable in other projects is good. Also a good way of thinking about Apps in Django provide modern web applications.
Imagine that you are creating big dynamic web app basing on JavaScript.
You can create then in django App named e.g "FrontEnd" <-- in thins app you will display content.
Then you create some backend Apps. E.g App named "Comments" that will store user comments. And "Comments" App will not display anything itself. It will be just API for AJAX requests of your dynamic JS website.
In this way you can always reuse your "Comments" app. You can make it open source without opening source of whole project. And you keep clean logic of your project.