我在Python中所有的.csv文件都将转换为excel文件df.to_csv'stock_dfs / {}csv'.formatticker

我正在运行此代码，它可以正常工作，但是它转换后的文件应该是.csv，但是我在文件夹中的所有文件都是excel。我不确定此错误是否与代码有关。但不胜感激。

import bs4 as bs
import datetime as dt
import os
import pandas as pd
from pandas_datareader import data as pdr
import pickle
import requests
import yfinance as yf

yf.pdr_override()

def save_sp500_tickers():
    resp = requests.get('https://en.wikipedia.org/wiki/List_of_S%26P_500_companies')
    soup = bs.BeautifulSoup(resp.text,"lxml")
    table = soup.find('table',{'class':'wikitable sortable'})
    tickers = []
    for row in table.findAll('tr')[1:]:
        ticker = row.findAll('td')[0].text.replace('.','-')
        ticker = ticker[:-1]
        tickers.append(ticker)
    with open("sp500tickers.pickle","wb") as f:
        pickle.dump(tickers,f)
    print(tickers)
    return tickers

#save_sp500_tickers()

def get_data_from_yahoo(reload_sp500=False):
    if reload_sp500:
        tickers = save_sp500_tickers()
    else:
        with open("sp500tickers.pickle","rb") as f:
            tickers = pickle.load(f)
    if not os.path.exists('stock_dfs'):
        os.makedirs('stock_dfs')
    start = dt.datetime(2019,6,8)
    end = dt.datetime.Now()
    for ticker in tickers[:20]:
        print(ticker)
        if not os.path.exists('stock_dfs/{}.csv'.format(ticker)):
            df = pdr.get_data_yahoo(ticker,start,end)
            df.reset_index(inplace=True)
            df.to_csv('stock_dfs/{}.csv'.format(ticker))
        else:
            print('Already have {}'.format(ticker))

save_sp500_tickers()
get_data_from_yahoo()