def read_csv(csv_name, usecols=None):
    """Returns a DataFrame from a .csv file stored in /data/raw/"""
    csv_path = os.path.join(DATA_FOLDER, csv_name)
    csv = pd.read_csv(csv_path, low_memory=False,
                      usecols=usecols, encoding="utf-8")
    return csv
Returns a DataFrame from a .csv file stored in /data/raw/