Unzip filename to a temporary directory, set to the cwd.

    The unzipped target is cleaned up after.

def archive_context(filename):
    """
    Unzip filename to a temporary directory, set to the cwd.

    The unzipped target is cleaned up after.
    """
    tmpdir = tempfile.mkdtemp()
    log.warn('Extracting in %s', tmpdir)
    old_wd = os.getcwd()
    try:
        os.chdir(tmpdir)
        try:
            with ContextualZipFile(filename) as archive:
                archive.extractall()
        except zipfile.BadZipfile as err:
            if not err.args:
                err.args = ('', )
            err.args = err.args + (
                MEANINGFUL_INVALID_ZIP_ERR_MSG.format(filename),
            )
            raise

        # going in the directory
        subdir = os.path.join(tmpdir, os.listdir(tmpdir)[0])
        os.chdir(subdir)
        log.warn('Now working in %s', subdir)
        yield

    finally:
        os.chdir(old_wd)
        shutil.rmtree(tmpdir)