def exchange(start_date, end_date):

        ex = pd.DataFrame()

        getdate = pd.date_range(start= str(start_date) , end = str(end_date)).to_series()

        getdate2 = getdate[getdate.apply(lambda x: x.weekday() != 6)]

        getdate = getdate2.apply(lambda x: x.strftime("%Y%m%d")).to_list()    

        for day in getdate:

            url = 'https://www.koreaexim.go.kr/site/program/financial/exchangeJSONauthkey=saPiIxk9gPEc9xqcqaXZL4UXXUWQ6oV7&searchdate='+f"{day}"+'&data=AP01'

            response = pd.read_json(requests.get(url).text)

            response['numeric'] = day

            ex = pd.concat([ex,response])

            ex1 = ex.rename(columns={'cur_unit':'country','deal_bas_r':'value'})

            ex1['value'] = ex1['value'].str.replace(pat=r',',repl=r'',regex=True).apply(float)

            exa = ex1[ex1['country']=='USD']

            exa['value_rate1'] = exa['value'].shift()

            exa['netchange'] = round(((exa['value'] - exa['value_rate1'])/exa['value_rate1'])*100,2)

            exa = exa.tail(1)

            exb = ex1[ex1['country']=='EUR']

            exb['value_rate1'] = exb['value'].shift()

            exb['netchange'] = round(((exb['value'] - exb['value_rate1'])/exb['value_rate1'])*100,2)



            exb = exb.tail(1)


    


            exc = ex1[ex1['country']=='JPY(100)']


            exc['value_rate1'] = exc['value'].shift()


            exc['netchange'] = round(((exc['value'] - exc['value_rate1'])/exc['value_rate1'])*100,2)


            exc = exc.tail(1)


    


            exd = ex1[ex1['country']=='CNH']


            exd['value_rate1'] = exd['value'].shift()


            exd['netchange'] = round(((exd['value'] - exd['value_rate1'])/exd['value_rate1'])*100,2)


            exd = exd.tail(1)


    


            exall = pd.concat([exa,exb,exc,exd])


        exall = exall.drop(columns={'value_rate1'})


        exall = exall[['value','netchange','numeric','country']]


        return exall



	



공부중인데


이걸 실행하면


UnboundLocalError: local variable 'exall' referenced before assignment


오류가 발생하는데..


한줄씩 실행하면 문제가 없단말야


뭐가 문제고 어떻게 고쳐야하는거야??