Dangers of decorator-based registries in Python

david@systemoverlord.com (David Tomaschik) — Sun, 26 Oct 2014 18:51:13 +0000

So Flask has a really convenient mechanism for registering handlers, actions to be run before/after requests, etc. Using decorators, Flask registers these functions to be called, as in:

#!python
@app.route('/')
def homepage_handler():
 return 'Hello World'

@app.before_request
def do_something_before_each_request():
 ...

This is pretty convenient, and works really well, because it means you don’t have to list all your routes in one place (like Django requires) but it comes with a cost. You can end up with Python modules that are only needed for the side effects of importing them. No functions from those modules are directly called from your other modules, but they still need to be imported somewhere to get the routes registered.

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Dangers of decorator-based registries in Python