Utility to add cache busting query parameter to all static elements on a site.

cache_buster.py

import hashlib
import os
from typing import Optional

from pyramid.request import Request
from pyramid.response import Response


def build_cache_id(
    filename: str,
    dev_mode: bool,
    file_hashes: dict,
    folder_path: str,
    log_hash_operations: bool
):
    if not filename:
        return 'ERROR_NO_FILE'

    file_lw = filename.strip().lower()
    if not dev_mode and file_lw in file_hashes:
        return file_hashes[file_lw]

    if log_hash_operations:
        print('Building new hash for ' + file_lw)

    fullname = os.path.abspath(os.path.join(folder_path, filename.lstrip('/')))

    if not os.path.exists(fullname):
        if log_hash_operations:
            print('Failed to generate hash for MISSING file ' + fullname)
        return 'ERROR_MISSING_FILE'
    if os.path.isdir(fullname):
        if log_hash_operations:
            print('Failed to generate hash for MISSING file ' + fullname)
        return 'ERROR_IS_DIRECTORY'

    file_hashes[file_lw] = get_file_hash(fullname)

    return file_hashes[file_lw]


def get_file_hash(filename: str) -> str:
    md5 = hashlib.md5()

    with open(filename, 'rb') as fin:
        data = fin.read()
        md5.update(data)

    return md5.hexdigest()[-6:]


def cache_response(
    request: Request,
    is_dev_mode: bool,
    seconds: int = 60,
    in_browser_only: bool = True,
    response: Optional[Response] = None,
):
    if is_dev_mode:
        return

    vis = 'private' if in_browser_only else 'public'
    request.response.headers['Cache-Control'] = f'{vis}, max-age={seconds}'

    if response:
        response.headers['Cache-Control'] = f'{vis}, max-age={seconds}'

Example usage in Chameleon:

<link href='$/static/css/landing-page.css?cache_id=${view.build_cache_id("/static/css/landing-page.css")}' rel="stylesheet">