def iter_format_modules(lang):
    """
    Does the heavy lifting of finding format modules.

    """
    if check_for_language(lang):
        format_locations = []
        for path in CUSTOM_FORMAT_MODULE_PATHS:
            format_locations.append(path + '.%s')
        format_locations.append('django.conf.locale.%s')
        locale = to_locale(lang)
        locales = [locale]
        if '_' in locale:
            locales.append(locale.split('_')[0])
        for location in format_locations:
            for loc in locales:
                try:
                    yield import_module('.formats', location % loc)
                except ImportError:
                    pass
Does the heavy lifting of finding format modules.