Flask webassets integration.

Hello there, I think that webassets and the related Flask module are awesome and just had a few questions about the way files are read and structured within a Flask project.

Suppose we wish to keep track of 3 item types:

1. Non-compiled assets (e.g. LESS CSS, Stylus, Coffeescript .etc)
2. Compiled assets (e.g. CSS, JS)
3. Third party libraries used in a project (e.g. jQuery, Twitter Bootstrap)

I think a suitable directory structure would probably look something like this:

flask_project/assets/less/...   <- (1) Non-compiled assets
flask_project/assets/coffee/... <- (1) Non-compiled assets
flask_project/static/js/...     <- (2) Compiled assets
flask_project/static/js/...     <- (3) 3rd Party Libraries
flask_project/static/css/...    <- (2) Compiled assets
flask_project/static/css/...    <- (3) 3rd Party Libraries

I have been experimenting with Flask-Assets and can't seem to find a way to achieve this without doing something like this in the template:

{% assets filters="less", output="css/style.css",
          "../assets/less/style.less", "../assets/less/import.less" %}
    <link rel="stylesheet" type="text/css" media="screen" href="{{ ASSET_URL }}" />
{% endassets %}

I also attempted to use the ASSETS_LOAD_PATH config item but didn't have any luck.

Is there any way to specify the source directory independently from the destination directory?

Also another little question, is the cache really needed? For example, I pictured that it would work as follows.

1. I update my non-compiled source
2. The hash is saved in a dict (or similar)
3. An output file is generated
4. Next time I refresh the page, the hash is calculated against each file and compared to the value in the dict
5. If it has changed, repeat steps above

Please let me know your thoughts and if I'm missing something :)

Thank you so much and keep up the great work! Fotis

Fixes the flask-assets ManageCommand for building. The Environment instance found is the environment itself, which does not have an attribute "environment". If I am simply using this wrong (i have tried letting it find my environment as well) please let me know

I have other packages in my environment having a requirement for the webassets package. These upgrade webassets to 0.9. And then while running pip installs with the --upgrade flag, I face an error which says:

error: Installed distribution webassets 0.9 conflicts with requirement webassets==0.8

On deeper probe, I figured it is flask-assets which has a specified dependency on webassets==0.8.

vagrant@dev:/usr/local/lib/python2.7/dist-packages$ sudo grep -r ==0.8 *
Flask_Assets-0.8-py2.7.egg/EGG-INFO/requires.txt:webassets==0.8

Any particular problem that holds flask-assets back from supporting webassets latest version?

As far as I can see the Flask-Script 0.6 is not supported. Running command results in

Traceback (most recent call last):
  File "manage.py", line 15, in <module>
    manager.run()
  File "/blah/blah/blah/python2.7/site-packages/flask_script/__init__.py", line 366, in run
    raise e
TypeError: create_parser() got an unexpected keyword argument 'parents'

Heya, this references issue #19. I thought I'd submit this pull request, which adds a Jinja2TemplateFilter to flask-assets (exposed under the name jinja2template). It is automatically registered when flask_assets is imported, so it should be usable out of the box.

This obviously requires the latest development release of webassets to run (since I just got my initial jinja2 filter accepted there), so I'm not sure if you'd like to merge this now, or wait till webassets makes a new stable release.

Either way, I thought I'd leave this here to see what you think.

Currently the latest stable release is not compatible with how Flask handles the exception, see this commit: 006864bc969cdc17d879635f94683d4d374305d1.

So we can’t use ManageAsset() with Flask-Script for example.

The fix is already present in master, when will you push the next major version?

In response to Issue #45, this commit adds support for use with the Flask S3 extension.

To use, add a config variable FLASK_ASSETS_USE_S3 and set it to True, for example

app.config['FLASK_ASSETS_USE_S3'] = True

A full example can be seen here.

Small caveat: Anytime you change a bundle, you must run something to the effect of

from app import app
import flask_s3
flask_s3.create_all(app)

in order for the new changes to be pushed to S3. It is also recommended to use versioning within the filename rather than the query string when using with CloudFront, (you can tell CloutFront to recognize unique query strings, but it's not recommended), as is done in the above example. Also note that if you want to use CloutFront, you will need to install Flask S3 from my fork until this pull request is merged in.

If you setup your Flask installation as describe here: http://flask.pocoo.org/docs/patterns/packages/#modules-and-resources, flask-assets isn't able to find static files stored in the module's static directory.

I am getting the following error when I try to build assets using the --parse-templates option. Im not really sure where to start debugging this...

Searching templates...
Traceback (most recent call last):
  File "/Users/joe/Sites/_projects/words/venv3/lib/python3.4/site-packages/jinja2/nodes.py", line 386, in as_const
    return f(self.left.as_const(eval_ctx), self.right.as_const(eval_ctx))
  File "/Users/joe/Sites/_projects/words/venv3/lib/python3.4/site-packages/jinja2/nodes.py", line 365, in as_const
    raise Impossible()
jinja2.nodes.Impossible

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/joe/Sites/_projects/words/venv3/lib/python3.4/site-packages/jinja2/nodes.py", line 386, in as_const
    return f(self.left.as_const(eval_ctx), self.right.as_const(eval_ctx))
  File "/Users/joe/Sites/_projects/words/venv3/lib/python3.4/site-packages/jinja2/nodes.py", line 388, in as_const
    raise Impossible()
jinja2.nodes.Impossible

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "manage.py", line 110, in <module>
    manager.run()
  File "/Users/joe/Sites/_projects/words/venv3/lib/python3.4/site-packages/flask_script/__init__.py", line 412, in run
    result = self.handle(sys.argv[0], sys.argv[1:])
  File "/Users/joe/Sites/_projects/words/venv3/lib/python3.4/site-packages/flask_script/__init__.py", line 383, in handle
    res = handle(*args, **config)
  File "/Users/joe/Sites/_projects/words/venv3/lib/python3.4/site-packages/flask_script/commands.py", line 216, in __call__
    return self.run(*args, **kwargs)
  File "/Users/joe/Sites/_projects/words/venv3/lib/python3.4/site-packages/flask_assets.py", line 422, in run
    return impl.main(args)
  File "/Users/joe/Sites/_projects/words/venv3/lib/python3.4/site-packages/webassets/script.py", line 557, in main
    return self.run_with_argv(argv)
  File "/Users/joe/Sites/_projects/words/venv3/lib/python3.4/site-packages/webassets/script.py", line 549, in run_with_argv
    return self.run_with_ns(ns)
  File "/Users/joe/Sites/_projects/words/venv3/lib/python3.4/site-packages/webassets/script.py", line 531, in run_with_ns
    env = self._setup_assets_env(ns, log)
  File "/Users/joe/Sites/_projects/words/venv3/lib/python3.4/site-packages/flask_assets.py", line 364, in _setup_assets_env
    env.add(*[b for b in self.load_from_templates(env, ns.jinja_extension)
  File "/Users/joe/Sites/_projects/words/venv3/lib/python3.4/site-packages/flask_assets.py", line 391, in load_from_templates
    load_bundles()
  File "/Users/joe/Sites/_projects/words/venv3/lib/python3.4/site-packages/webassets/ext/jinja2.py", line 218, in load_bundles
    bundles.extend(self.with_file(filename, self._parse) or [])
  File "/Users/joe/Sites/_projects/words/venv3/lib/python3.4/site-packages/webassets/loaders.py", line 301, in with_file
    return then_run(filename, contents)
  File "/Users/joe/Sites/_projects/words/venv3/lib/python3.4/site-packages/webassets/ext/jinja2.py", line 246, in _parse
    _recurse_node(node)
  File "/Users/joe/Sites/_projects/words/venv3/lib/python3.4/site-packages/webassets/ext/jinja2.py", line 244, in _recurse_node
    _recurse_node(node)
  File "/Users/joe/Sites/_projects/words/venv3/lib/python3.4/site-packages/webassets/ext/jinja2.py", line 237, in _recurse_node
    *AssetsExtension.resolve_contents(files.as_const(), self.asset_env),
  File "/Users/joe/Sites/_projects/words/venv3/lib/python3.4/site-packages/jinja2/nodes.py", line 490, in as_const
    return [x.as_const(eval_ctx) for x in self.items]
  File "/Users/joe/Sites/_projects/words/venv3/lib/python3.4/site-packages/jinja2/nodes.py", line 490, in <listcomp>
    return [x.as_const(eval_ctx) for x in self.items]
  File "/Users/joe/Sites/_projects/words/venv3/lib/python3.4/site-packages/jinja2/nodes.py", line 388, in as_const
    raise Impossible()
jinja2.nodes.Impossible

@miracle2k This has gotten a bit out of hand. There are 3 open issue open that have to do with the inability to get the correct version of of webassets. Moreover, it has made it quite difficult to get new installations up and breaks builds.

The cleanest solution is to eliminate the parse_version function in setup.py entirely and simply update the specific version in setup.py as things progress. As stated in the Zen of Python, "Explicit is better than implicit", "Simple is better than complex", and "Readability counts". Unfortunately, right now I think this setup is in contradiction with each of these.

Before version 0.8, flask used flaskext namespace: http://flask.pocoo.org/docs/extensions/#flask-before-0-8 But with 0.8 this behaviour was changed.

Probably, major version's increment needed. Otherwise, backward compatibility could be added, using:

import flaskext_compat
flaskext_compat.activate()
from flask.ext import script

Looks like flask-assets will not work in flask-2.3 and on:

.venv/lib/python3.11/site-packages/flask_assets.py:8
.venv/lib/python3.11/site-packages/flask_assets.py:8
  /Users/patrick/dev/triplynx3/.venv/lib/python3.11/site-packages/flask_assets.py:8: DeprecationWarning: '_request_ctx_stack' is deprecated and will be removed in Flask 2.3.
    from flask import _request_ctx_stack, current_app

.venv/lib/python3.11/site-packages/flask_assets.py:317: 11 warnings
tests/test_home.py: 239 warnings
  /Users/patrick/dev/triplynx3/.venv/lib/python3.11/site-packages/flask_assets.py:317: DeprecationWarning: '_request_ctx_stack' is deprecated and will be removed in Flask 2.3. Use 'g' to store data, or 'request_ctx' to access the current context.
    ctx = _request_ctx_stack.top

.venv/lib/python3.11/site-packages/flask_assets.py:322: 22 warnings
  /Users/patrick/dev/triplynx3/.venv/lib/python3.11/site-packages/flask_assets.py:322: DeprecationWarning: '_app_ctx_stack' is deprecated and will be removed in Flask 2.3.
    from flask import _app_ctx_stack

.venv/lib/python3.11/site-packages/flask_assets.py:323: 11 warnings
  /Users/patrick/dev/triplynx3/.venv/lib/python3.11/site-packages/flask_assets.py:323: DeprecationWarning: '_app_ctx_stack' is deprecated and will be removed in Flask 2.3. Use 'g' to store data, or 'app_ctx' to access the current context.
    app_ctx = _app_ctx_stack.top

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html

I'm using the library with the template only method:

{% assets filters="jsmin", output="gen/packed.js",
          "common/jquery.js", "site/base.js", "site/widgets.js" %}
    <script type="text/javascript" src="{{ ASSET_URL }}"></script>
{% endassets %}

But I'm having an issue with the jsmin library stripping whitespace in my template strings, so that this is a test is turned into thisisatest. The jsmin library has the quote_chars=quote_chars="'\"`" parameter that should fix this, is there a way to pass the parameter to the template?

Would be great if flask-assets could be statically type checked with: https://mypy.readthedocs.io/en/stable/running_mypy.html#missing-type-hints-for-third-party-library

According to the flask-assets documentation about blueprints, a path prefix is used to denote the use of blueprint-specific static folders when defining bundles. However, this caused issues for my project, because I'm using a single shared {APP_ROOT}/static directory for all blueprints, in which I also have subdirectories; so if there's a subdirectory with the same name as a blueprint, flask-assets would give me an TypeError: The referenced blueprint <flask.blueprints.Blueprint object at ...> has no static folder., because it would look for a blueprint-specific static folder {BLUEPRINT_ROOT}/static. In my case, I had a 'debug' blueprint for testing purposes and a 'debug' subdirectory within my {APP_ROOT}/static. The doc states

If you are using Flask blueprints, you can refer to a blueprint’s static files via a prefix, in the same way as Flask allows you to reference a blueprint’s templates

but I'm not sure the statement about Flask's way of referencing templates is (still) true; when I reference templates in my project, they're always interpreted as paths beneath the app root template directory or the specific blueprint template directory, so the blueprint name is never part of the template path either way.

The ambiguity of the first part of a bundle source path being interpreted as either a blueprint (but only if a blueprint of that name exists) or a subdirectory seems confusing to me. There might be ways to entirely circumvent that using flask-assets or Flask configurations or even the right parameters for the bundle, but I couldn't find what I was looking for in the docs. I'm sorry if I missed a solution that I could I have gotten by looking into it more carefully.

I'm not sure if there's a better way to do this (maybe a blueprint keyword argument in the Bundle constructor, which would apply to all input and output files though, or some other way to denote the use of blueprints on a file-by-file base), but I just wanted to point out that this can lead to some confusion or potentially to unnecessary limitations on how to name things in the project.

Flask.static_path has been removed in Flask 1.0. See pallets/flask#2385.

Also, Flask.static_folder does not work as expected when the path ends in a trailing slash. See pallets/flask#3452.