为什么在 python 中嵌套 for 循环只获取最后一项，有时倒数第二个

Question

我想在 coin_heads 循环中使用 for coin 遍历 coin_heads 列表，它在其他循环中

exchange_names = ['binance','huobi','bybit', 'kraken', 'bitso', 'bitfinex', 'poloniex', 'bitget', 'bitmex', 'bitstamp', \
                   'bittrex', 'kucoin', 'phemex','okx','gate','bitmart','mexc','bitvavo','wavesexchange','xt']
coin_heads = ['XRP','ADA','DOGE','MATIC','SOL','DOT','TRX']

update_interval = 2  # seconds


async def find_arbitrage_opportunities():

    
    exchanges = []
    for name in exchange_names:
        exchange = getattr(ccxt, name)()
        await exchange.load_markets()
        exchanges.append(exchange)
        

    while True:
       
        ticker_coinhead = {}
        ticker_prices = {}
        for exchange in exchanges:
            for coin in coin_heads:
                try:
                    ticker = await exchange.fetch_ticker(f'{coin}/USD')
                    ticker_prices[exchange.id] = ticker['last']
                    ticker_coinhead[exchange.id] = coin
                except ccxt.errors.ExchangeError:
                    pass

 for i in range(len(exchanges)):
            for j in range(len(exchanges)):
                if i != j:
                    exchange1 = exchanges[i]
                    exchange2 = exchanges[j]
                    if exchange1.id in ticker_prices and exchange2.id in ticker_prices:
                        rate1 = ticker_prices[exchange1.id]
                        rate2 = ticker_prices[exchange2.id]
                        if rate1 > rate2:
                            profit_percentage = (rate1 / rate2 - 1) * 100
                            if profit_percentage > 2:
                                print(f"\033[92mArbitrage opportunity found between {exchange1.id} ({rate1}) and {exchange2.id} ({rate2}) for {ticker_coinhead[exchange1.id]} coinhead:: {profit_percentage}%\033[0m")
                            else:
                                print(f"Arbitrage opportunity found between {exchange1.id} ({rate1}) and {exchange2.id} ({rate2}) for {ticker_coinhead[exchange1.id]} coinhead: {profit_percentage}%")

        await asyncio.sleep(update_interval)

出于某种原因，输出只提供列表最后一个元素的信息，有时它会比较列表的最后两个元素，但它不应该

Arbitrage opportunity found between bitstamp (5.783) and bittrex (0.0706) for DOT coinhead:: 8091.218130311616%
Arbitrage opportunity found between bitstamp (5.783) and gate (0.0704418) for DOT coinhead:: 8109.614177945483%
Arbitrage opportunity found between bittrex (0.0706) and binance (0.07043) for TRX coinhead: 0.24137441431206774%
Arbitrage opportunity found between bittrex (0.0706) and kraken (0.070447) for TRX coinhead: 0.21718455008730153%
Arbitrage opportunity found between bittrex (0.0706) and bitso (0.070406) for TRX coinhead: 0.2755446978950582%

好吧，预计要比较来自不同交易所的同一个硬币输出的几个不同的硬币