[Python] next () only keeps accessing the last bars of the datas[1]

When i tried to import multiple csv files into self.data using backtrader, except for the first datas[0], the rest of the dataset accessed only the last bar in the next() function These are the two data sets I tested(same form):

enter code here
datetime open ... volume openintrest
datetime ...
2025-01-17 06:00:00 2025-01-17 06:00:00 100156.98 ... 287.20439 0
2025-01-17 06:30:00 2025-01-17 06:30:00 99596.80 ... 256.37462 0
2025-01-17 07:00:00 2025-01-17 07:00:00 99838.25 ... 498.32045 0
2025-01-17 07:30:00 2025-01-17 07:30:00 99891.23 ... 161.58102 0
2025-01-17 08:00:00 2025-01-17 08:00:00 99987.30 ... 531.72307 0


Here is the simpfiy code:

enter code here
from datetime import timedelta, datetime
import ccxt
import backtrader as bt
import pandas as pd
import os

class TestStrategy(bt.Strategy):

def __init__(self):#计算指标
self.dataclose=self.datas[1].lines.open
def next(self):#调用指标和策略
dt = self.datas[1].lines.datetime.date(0)
self.log(dt,self.dataclose[0])
def log(self,dt,text):
print(dt,text)

if __name__=='__main__':
cerebro = bt.Cerebro()
since_time = datetime(year=2024, month=11, day=1)
to_time = datetime(year=2025, month=4, day=1)
file_path = ["E:/PycharmProjects/PythonProject/backtrader/data/2025-01-28 15：30：
00.csv",
"E:/PycharmProjects/PythonProject/backtrader/data/2025-01-16 22：00：
00.csv"]
for i in file_path:#Two data sets are imported
df = pd.read_csv(i, parse_dates=['datetime']) # 将 datetime 列解析为日期时间类型
df.index = pd.to_datetime(df.datetime)
df['openintrest'] = 0
df = df[['open', 'high', 'low', 'close', 'volume', 'openintrest']]
data = bt.feeds.PandasData(
dataname=df,
fromdate=since_time,
todate=to_time,
)
cerebro.adddata(data)


cerebro.addstrategy(TestStrategy)
cerebro.run


When I try to access the first dataset:

enter code here
class TestStrategy(bt.Strategy):

def __init__(self):#计算指标
self.dataclose=self.datas[0].lines.open
def next(self):#调用指标和策略
dt = self.datas[0].lines.datetime.date(0)
self.log(dt,self.dataclose[0])
def log(self,dt,text):
print(dt,text)


The result output is:

enter code here
2025-01-17 99596.8
2025-01-17 99838.25
2025-01-17 99891.23
2025-01-17 99987.3
2025-01-17 100156.0
2025-01-17 100120.58


But try to access the second dataset:

enter code here
class TestStrategy(bt.Strategy):

def __init__(self):#计算指标
self.dataclose=self.datas[1].lines.open
def next(self):#调用指标和策略
dt = self.datas[1].lines.datetime.date(0)
self.log(dt,self.dataclose[0])
def log(self,dt,text):
print(dt,text)


The output is:

enter code here
2025-01-15 98729.41
2025-01-15 98729.41
2025-01-15 98729.41
2025-01-15 98729.41
2025-01-15 98729.41
2025-01-15 98729.41


next () only keeps accessing the last bar of the datas[1] date. If there is anything unclear, please point out, thank you for your help

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