def lookup_nimby_value(date_key, letter, df_prop):
    """Look up the value for the nimby variable value. 
    Args: 
        date_key (str): code with election date
        letter (str): proposition letter
        df_prop (DataFrame): the proposals dataframe
    """

    return(df_prop[(df_prop.Date_str==date_key)&(df_prop.Letter==letter)]['Vote that equals NIMBY'].values[0])