My experience of Flask is not as extensive as my experience of Django, but still recently I’ve developed some of my projects with Flask and I could not help comparing those 2 Python web frameworks. This will be a quick comparison which will not focus on code but rather on “philosophical” considerations. Of course my opinion might change in the future!
Both Are Still Python Frameworks
When I switched from Django to Flask, what first occurred to me was that a lot of things are very similar. You won’t be lost. This is mainly due to the fact that both are using Python. Even if Flask is supposed to be more Pythonic (using decorators extensively for example), I did not notice many differences. In addition to that, both are web frameworks and most of web frameworks propose pretty much the same features:
- an ORM
- routing features
- a user request object used extensively
- templates
- forms handling
- static files handling
- …
Even if you switch from Python to another language, using a web framework will help you a lot because this MVC structure will be there (ok this is not always real MVC but whatever) and you will be at home in a second. For example see how easy it is to switch from Python/Django to PHP/Laravel.
Framework VS Micro Framework
Flask is supposed to be a micro framework which is less “opinionated” and with less “batteries included”. In a way you’re supposed to be more free than with Django. And this is true! Django proposes a file/folder structure that everyone follows. Django also ships with its own ORM, templating system, forms handling, registration/login system,… which are used by 99% of people. Problem is that, in my opinion, this freedom is more of a problem than an help…
This lack of structure implies that you know in advance exactly what will be the best structure for your project, which is very difficult if you have never developed a full project with Flask yet and never had the opportunity to test how this structure will fit a growing project over months/years. I saw a lot people ending up asking for advice regarding their project structure on StackOverflow and eventually most people use… Django’s structure (one central configuration file and one folder per application containing a views.py + models.py + forms.py + templates)! I also struggled, like many people, with Python circular imports, which never happens in Django since smart people designed the structure for you in advance especially in order to avoid this kind of problems.
Project’s structure is a very important part of a project’s documentation. A standard structure will considerably help newcomers on your project. Every time I start working on an existing Django project, I am fully operational in a minute because I know in advance how things are organized. It is not the case with Flask so developers on a Flask project need to write additional documentation to explain their project’s structure. Same problem with tooling: every Flask project might ship with different core libraries (for forms, templates, registration/login, etc.) so new developers arriving on a project might have to learn new tools before starting working.
Documentation
Flask’s documentation is good but it is clearly too hard for beginner developers compared to Django’s docs which matches every levels (from beginner to advanced). In addition to that, Flask being a micro framework, most of your work relies on external dependencies like SQLAlchemy for ORM, Flask login for login, Flask WTF for forms, etc. and some of these libs do not have the same documentation standard as Flask does. Let me put it this way: I find SQLAlchemy’s docs awful, and tools like Flask login really need to grow their docs for example (solving my problems by browsing the lib’s source code should never happen in my opinion).
Community
Flask’s community is much smaller than Django’s (but very nice). Consequence is that you won’t find all your answers on StackOverflow or GitHub. However you end up realizing that most issues are actually Python issues (so no problem here) or issues met by Django’s users as well (so in this case Django’s community helps).
Conclusion
Flask is a micro framework that does not recommend standards or conventions. In my opinion this is more of a problem than a solution if you want your project to be easily maintained by other people. However if freedom attracts you, then give Flask a try! If you’re already a Django developer the switch will be super easy.