When comparing Flask vs Bottle, the Slant community recommends Flask for most people. In the question“What are the best backend web frameworks?” Flask is ranked 7th while Bottle is ranked 20th. The most important reason people chose Flask is:
Flask is very easy to get up and going, with vanilla HTML or with bootstrap pieces. It doesn't take much lines of Python to load Flask to get headers working, etc, and since it's all modular you don't have to have something you don't want in your application.
Specs
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Pros
Pro Minimalist without losing power
Flask is very easy to get up and going, with vanilla HTML or with bootstrap pieces. It doesn't take much lines of Python to load Flask to get headers working, etc, and since it's all modular you don't have to have something you don't want in your application.
Pro Lots of resources available online
Flask is one of the most popular Python web frameworks, if not the most popular one. As such, there's plenty of guides, tutorials, and libraries available for it. A large number of important Python libraries, such as SQLAlchemy have libraries for Flask, which add valuable bindings to make the development process and the integration between these libraries and Flask as easy as possible.
Pro Extremely easy to build a quick prototype
Even though it's pretty minimalistic out of the box, Flask still provides the necessary tools to build a quick prototype for a web app right after a fresh install. With all the main components pretty much packed in the flask
package, building a simple web app in a single Python file is as easy as it gets.
Pro Very flexible
Flask gives developers a lot of flexibility in how they develop their web applications.
For example, the choice of not having an ORM, but instead choosing one suited to the task, or another area where Flask gives a lot of options to developers is the templating. They can use Jinja2, Flask's default templating language or choose from a number of different templating languages they desire.
Pro Great documentation
The official documentation is very thorough and complete. Everything is explained in-depth and followed by extremely well-explained tutorials that tackle real-world problems.
Pro Able to use ORM or "true SQL"
Pro Flexible
Being a small one file distribution it includes almost every vital thing you need to support little websites (routing, templating). Everything else can be implemented using plugins.
Pro Single-file distribution
Bottle works around the one-file approach, everything is done in a bottle.py
file. This means that it's extremely easy to share and upload your application since it practically is just one python file.
Pro No need to install
It is so little there's no need to install, it is included in the standard libs python.
Pro Async, *let friendly
Using it with gevent is a breeze. It's a WSGI app so it's easy to make it work with anything.
Pro Truly magnificent
Cons
Con Not async-friendly
Flask is explicitly not designed to handle async programming.
Con Setting up a large project requires some previous knowledge of the framework
Setting up a large project with Flask is not that easy considering how there's no "official" way of doing it. Blueprints are a useful tool in this regard but require some additional reading and are a bit tricky to get right for a beginner.
The lack of some defaults can also be problematic. Having to choose between different libraries for a certain task is never easy, especially if you have never worked with Flask before.
Con Threadlocals and globals used everywhere
The default way of creating applications in flask makes it hard to use reusable and clean code.
Con HTML-oriented, not API-oriented
Not necessarily designed for making APIs, though that is possible
Con Small community. Difficult to find online docs and examples
Con Very hard to develop projects that are not smaller than 1000 lines
While Bottle is a great framework for building small applications (generally less than 1000 lines of code), it starts getting very hard to manage your application if you want to go even a bit larger than that.
The fact that it follows a single-file distribution model and that it's missing something like Flask's blueprints only make this problem worse.