I would like to include a sass compiler in my Flask application. Is there a generally accepted way of doing this?

Flask-Assets extension (which uses webassets library) can be used for that. Here's how to configure it to use pyScss compiler (implemented in Python) for SCSS:

from flask import Flask, render_template
from flask.ext.assets import Environment, Bundle

app = Flask(__name__)

assets = Environment(app)
assets.url = app.static_url_path
scss = Bundle('foo.scss', 'bar.scss', filters='pyscss', output='all.css')
assets.register('scss_all', scss)

And in the template include this:

{% assets "scss_all" %}
<link rel=stylesheet type=text/css href="{{ ASSET_URL }}">
{% endassets %}

SCSS files will be compiled in debug mode as well.

pyScss only supports SCSS syntax, but there are other filters (sass, scss and compass) which use the original Ruby implementation.