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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def QA_fetch_get_sz_margin(date):
 """return shenzhen margin data Arguments: date {str YYYY-MM-DD} -- date format Returns: pandas.DataFrame -- res for margin data """


    if date in trade_date_sse:
        return pd.read_excel(_sz_url.format(date)).assign(date=date).assign(sse='sz')