Simple python script to add a query string to all css / js files using a unix timestamp to force refresh of static assets.

cachebuster.py

#!/usr/bin/env python
import time

def cachebust_script_src(line):
    src_i = line.find("src=")
    begin_src = src_i + 5
    end_src = line.find("\"", begin_src)
    src_contents = line[begin_src:end_src]
    parts = src_contents.split("?")
    base_src = parts[0]
    src_contents = base_src + "?" + str(int(time.time() * 1000))
    
    before_src = line[:src_i]
    after_src = line[end_src:]
    line = before_src + "src=\"" + src_contents + after_src
    return line

def cachebust_css_href(line):
    href_i = line.find("href=")
    begin_href = href_i + 6
    end_href = line.find("\"", begin_href)
    href_contents = line[begin_href:end_href]
    parts = href_contents.split("?")
    base_href = parts[0]
    href_contents = base_href + "?" + str(int(time.time() * 1000))
    
    before_href = line[:href_i]
    after_href = line[end_href:]
    line = before_href + "href=\"" + href_contents + after_href
    return line

def update_template_file(name):
    print "Updating template file:", name
    lines = []
    with open(name) as f:
        for line in f:
            if "<script" in line:
                line = cachebust_script_src(line)
            elif "rel=\"stylesheet\"" in line:
                line = cachebust_css_href(line)
            lines.append(line)

    with open(name, "w") as f:
        for line in lines:
            f.write(line)

if __name__ == "__main__":
    import sys
    if len(sys.argv) > 1:
        config_file = sys.argv[1]
    else:
        config_file = "cachebuster-conf.txt"

    with open(config_file) as f:
        for line in f:
            line = line.strip()
            update_template_file(line)