import gzip
import json


def get_pack(filepath):
    """Get a gzipped json file from the given path (specified without
    the '.json.gz' ending).
    Raises <FileNotFoundError> if the file doesn't exist.
    Returns the mapping.
    """
    fpath = filepath + '.json.gz'
    with gzip.open(fpath, 'rt', encoding='utf-8') as zipfile:
        data = json.load(zipfile)
    return data