Performance enhancement: run slimit/cssmin only when needed

[didip]

When I use cProfile to observe my minify_assets function, one thing is clear: method inside slimit is called often.

So I optimized the _process_bundle method to skipped files that ends with '.min.js' and '.min.css'. See the snippet below:

def _process_bundle(self, name, paths, type):
    sha1, sep = '', ''
    contents  = [open(path).read() for path in paths]
    raw_data  = ''.join(contents)

    if self.config.get('fingerprint'):
        sha1, sep = hashlib.sha1(raw_data).hexdigest(), '-'

    file_ext = {
        'javascript': '.js',
        'css': '.css',
        }.get(type)

    fname_template = '%s%s%s{suffix}%s{gz}' % (name, sep, sha1, file_ext)
    raw_fname = fname_template.format(suffix='', gz='')
    self.write(raw_fname, raw_data)

    # Minify only if asset haven't been minified previously
    minified_data = []
    for index, path in enumerate(paths):
        if type == 'javascript':
            if path.endswith('min.js'):
                minified_data.append(contents[index])
            else:
                minified_data.append(slimit.minify(contents[index], mangle=True))

        elif type == 'css':
            if path.endswith('min.css'):
                minified_data.append(contents[index])
            else:
                minified_data.append(cssmin.cssmin(contents[index]))

    minified_data = ''.join(minified_data)

The difference is staggering.

Before:

772394 function calls (761023 primitive calls) in 7.112 seconds

After:

181488 function calls (180859 primitive calls) in 0.766 seconds

I didn't change my assets.yml file. For example, jquery.min.js had always been included.

I also tried replacing slimit with other pure python js minifier before the optimization and the result is the same.

[rspivak]

Thanks for bringing it up. I think it can be beneficial to have a configuration option that allows one to provide a list of file patterns to exclude from processing.

[didip]

Sounds like a good idea.