Simple cache bust technique for Flask projects. `/static/main.css` becomes `/static/main.123456789.css`

__init__.py

import re
from flask import Flask
from flask.helpers import send_from_directory

# Subclass Flask and override send_static_file method
class CustomStaticFlask(Flask):

    def send_static_file(self, filename):
        """Overrides to filter out cache buster from file path
        Input images/file.{hash}.css
        Output images/file.css
        """
        if not self.has_static_folder:
            raise RuntimeError('No static folder for this object')

        # Replace cache bust key in filename
        cache_bust_enabled = self.config.get('STATIC_CACHEBUST_ENABLED')
        allowed_extensions = self.config.get('STATIC_CACHEBUST_EXTENSIONS')

        if cache_bust_enabled:
            filename = re.sub(r"\.(\d*)\.(" + allowed_extensions + ")$",
                              r".\2",
                              filename)

        cache_timeout = self.get_send_file_max_age(filename)
        return send_from_directory(self.static_folder, filename,
                                   cache_timeout=cache_timeout)

# Create your app based on the subclass
def create_app(config=None):
    app = CustomStaticFlask(__name__)

config.py

import os

class BaseConfig(object):
    STATIC_CACHEBUST_ENABLED = \
        os.environ.get("STATIC_CACHEBUST_ENABLED", "False") == "True"
    STATIC_CACHEBUST_EXTENSIONS = \
        os.environ.get("STATIC_CACHEBUST_EXTENSIONS",
                       "css|js|png|svg|jpg|jpeg")

manage.py

from flask import url_for

@app.context_processor
def override_url_for():
    return dict(url_for=dated_url_for)


def dated_url_for(endpoint, **values):
    cache_bust_enabled = app.config.get('STATIC_CACHEBUST_ENABLED')
    allowed_extensions = app.config.get('STATIC_CACHEBUST_EXTENSIONS')

    if endpoint == 'static':
        filename = values.get('filename', None)
        if filename:
            file_path = os.path.join(app.root_path,
                                     endpoint, filename)
            if os.path.exists(file_path):
                file_changed_timestamp = int(os.stat(file_path).st_mtime)
                filename_split = os.path.splitext(filename)
                extension_matches_allowed =\
                    re.match(r"\.(" + allowed_extensions + ")",
                             filename_split[1])
                if cache_bust_enabled and extension_matches_allowed:
                    cache_bust_key = ('.', str(file_changed_timestamp))
                    cache_bust_filename = \
                        (''.join(cache_bust_key)).join(filename_split)
                    values['filename'] = cache_bust_filename
    return url_for(endpoint, **values)