Issue using Flask-Assets to compile less files

Question

I'm currently trying to set up a Flask web app, and trying to use Flask-Assets to compile my less files into minified css.

Here is my assets.py file that creates the bundle.

from flask_assets import Bundle

common_css = Bundle(
    'vendor/less/theme.less',
    filters='less',
    output='static/css/common.css',
    )

The error that I am getting is:

OSError: [Errno 2] No such file or directory

In the webassets documentation for the less filter, it says that:

This depends on the NodeJS implementation of less, installable via npm. To use the old Ruby-based version (implemented in the 1.x Ruby gem), see Less.

...

LESS_BIN (binary)
    Path to the less executable used to compile source files. By default, the filter will attempt to run lessc via the system path.

I installed less using $ npm install less, but for some reason it looks like webassets can't use it.

When I try to use different filters, then webassets can successfully create the bundle.

Thanks!

Answer 1

npm install installs packages in current directory by default (you should be able to find node_modules directory there). You have two choices:

1. Install lessc globally:

   $ npm install -g less
   

   This way webassets will be able to find it itself.

2. Provide a full path to lessc executable:

   assets = Environment(app)
   assets.config['less_bin'] = '/path/to/lessc'
   

   The path should be <some_directory>/node_modules/.bin/lessc.