Finds and loads gulp's rev-manifest.json file.
    In default, this is looking for rev-manifest.json file places in your
    STATIC_ROOT. Can be overriden to a specific location by setting
    DJANGO_GULP_REV_PATH.

def _get_mapping():
    """
    Finds and loads gulp's rev-manifest.json file.
    In default, this is looking for rev-manifest.json file places in your
    STATIC_ROOT. Can be overriden to a specific location by setting
    DJANGO_GULP_REV_PATH.
    """
    global _STATIC_MAPPING

    if _STATIC_MAPPING is None:
        manifest_path = getattr(settings,
            'DJANGO_GULP_REV_PATH',
            os.path.join(getattr(settings, 'STATIC_ROOT', ''), 'rev-manifest.json'))
        
        try:
            with open(manifest_path) as manifest_file:
                _STATIC_MAPPING = json.load(manifest_file)
        except IOError:
            return None

    return _STATIC_MAPPING