Django custom storage backend that applies optimizations for png and jpg images

storage.py

from django.contrib.staticfiles.storage import CachedFilesMixin, StaticFilesStorage
from pipeline.storage import PipelineMixin


def coroutine(func):
    def start(*args, **kwargs):
        cr = func(*args, **kwargs)
        cr.next()
        return cr
    return start


class PipelineStorage(PipelineMixin, CachedFilesMixin, StaticFilesStorage):

    def post_process(self, paths, dry_run=False, **options):
        import shutil
        import re
        from fabric.api import local

        @coroutine
        def optimize(targets):
            while True:
                filename = (yield)
                # Do not optimize files that are less than 5Kb
                if 1024 * 4 < self.size(filename):
                    for target in targets:
                        target.send(filename)

        @coroutine
        def grep(pattern, target, inverse=False):
            pattern = re.compile(pattern)
            while True:
                filename = (yield)
                if pattern.match(filename):
                    print filename
                    target.send(filename)

        @coroutine
        def pngcrush():
            while True:
                filename = (yield)
                local('pngcrush -q '
                      '-rem gAMA -rem cHRM '
                      '-rem iCCP -rem sRGB '
                      '-rem alla -rem text '
                      '-reduce -brute "%s" "%s"' % (
                          self.path(filename),
                          '%s.min' % self.path(filename)
                          )
                )
                self.delete(filename)
                shutil.move('%s.min' % self.path(filename), self.path(filename))

        @coroutine
        def jpegtran():
            while True:
                filename = (yield)
                local('jpegtran '
                      '-outfile "%s" '
                      '-optimize '
                      '-copy none "%s"' % (
                          '%s.min' % self.path(filename),
                          self.path(filename)
                          )
                )
                self.delete(filename)
                shutil.move('%s.min' % self.path(filename), self.path(filename))

        def process(post_paths, target):
            for old_path, new_path, processed in post_paths:
                target.send(new_path)
                yield (old_path, new_path, processed)
                self.delete(old_path)
            target.close()

        post_paths = list(super(PipelineStorage, self).post_process(paths, dry_run, **options))

        new_paths = (process(post_paths, optimize([
                grep('.+\.png$', pngcrush()),
                grep('.+\.jpg$', jpegtran()),
            ])
        ))

        for old_path, new_path, processed in new_paths:
            new_path = self.hashed_name(new_path)
            yield (old_path, new_path, processed)