Flask is a server-side framework, so it’s not directly comparable to front-end frameworks like React or Angular. It plays a similar role to Rails in Ruby, Django in Python or Symfony in PHP, though it’s further towards the lightweight/flexible end of the spectrum than any of those.

I don’t know what you’d consider high traffic, but we have used and continue to use Flask in production for a variety of systems. Those include:

- providing the back ends for relatively large and complicated single-page applications;

- implementing more traditional web sites, with very little JS on the front end, which use Flask to do almost all of the routing and rendering; and

- implementing dedicated HTTP-based APIs for integration with third party services.

Flask is an excellent tool, and that is not a description I use for very much in the software world. It provides widely useful functionality, it has a tidy design and a reliable implementation, it’s well documented, and it imposes few overheads or unnecessary dependencies. If you’re purely a front-end dev then that functionality isn’t what you need and neither is Flask. If you’re interested in the back end as well, you could do a lot worse than to learn Flask.

Flask would be more comparable to RoR than to Angular, since it is principally for backend work. (You can do server-side-rendered front-end stuff with it, with templates, but I choose not to -- currently working with Flask for my backend API, React for frontend).

There are two main features of Flask for me, over something like RoR: it's Python (my preference over Ruby); and it's a very light framework with a ton of modules, compared to my perception that RoR is pretty big and heavy and opinionated.

YMV, I only do this stuff in my evenings so I'm not terribly familiar with it all.

Sinatra has always seemed more like the ruby equivalent of Flask, but I only have a small (and by now, dated) experience of ruby web dev

My Ruby developer friend agrees with you, so I think you're accurate.

You're comparing apples to oranges here. Flask is a server-side framework and doesn't care one whit about what you put on top - it just serves up requests.

We deploy a heavily used REST API that at the top level, is using Flask to capture/proxy/marshal the request and response. We decided to use it over Django simply because we did not need a large set of the Django features.

> I'm interested but when I look at job listings it's really rare I see anything for flask compared to [...] RoR.

That's because Flask is simple. You advertise RoR when you want somebody who doesn't need to spend a lot of time learning Rails. But nobody needs to spend a lot of time learning Flask.

That's also a drawback of Flask, in that you have to build or add more to get the same higher-level expressiveness of something like Rails. But if what the project needs is a relatively low-level web framework, it's a fine, easy-to-learn choice.

Reddit uses Flask for parts of the site.

Uber uses Flask & Nginx for part of their site.

The 2012 Obama campaign team (who really shook up the use of internet & tech in campaigning) used Flask too.

Mailgun uses Flask for their API (reported). Stack is verified here, but no details given: http://stackshare.io/mailgun/mailgun

Flask = backend

Angular = Front end

Bizarre you are comparing them. Suggests you have not used either.

I have no idea where you are looking for jobs but where I am demand for Flask and Django are booming and there is a shortage of them.

Not sure what kind of traffic they get, but httpbin.org uses it. Also this one site named Pinterest.

I am sorry, but it seems that Pinterest is written using Django.

https://www.djangoproject.com/start/overview/

Moved off Django to Flask.

https://www.quora.com/What-challenges-has-Pinterest-encounte...

That page does not support the statement that they moved off Django to Flask.

It further links to this post:

https://www.quora.com/What-is-the-technology-stack-behind-Pi...

> They started with Django but moved out of Django and currently use 'home grown framework on top of Flask'.

But it supports that they do use Flask.

> Presently, the API does over 12 billion requests per day, all in Flask.

Wow, that is 138kqps. Not something that would strike me as your typical Python workload.

There are lots of those lying around.

I don't know if it still is, but when I was at Mozilla the service that every instance of Firefox around the world hits to do the version/extension-compatibility checks was backed by Django, and was at something like 15k req/s served. Firefox has gained some market share in the four-ish years since I got that number, so probably larger now.

Whacking great big CDNs in front of your infra will do that.

What exactly a CDN can do to increase the qps throughput of your backend? I thought it's used to reduce it...

IIRC Twilio use Flask, and contributed the flask-restful library [1]

[1] https://github.com/flask-restful/flask-restful

Flask is a server-side framework, as others have mentioned.

You should be comparing it to micro web frameworks like Nodejs' Express, Ruby's Sinatra, PHP's Slim, Java's Spark, etc.