if we use code:
self.sma = bt.indicators.MovingAverageSimple(data, period)
self.sma[0] --> current bar
self.sma[-1] --> last one bar

But, I want it:
self.sma[0] --> current bar
self.sma[1] --> last one bar
Is there any other way besides the function ?

my code :

import backtrader as bt
cerebro = bt.Cerebro()
# ---read Data
Path = "C:\\Users\\i2011\\OneDrive\\Book_Code&Data\\量化投资以python为工具\\数据及源代码\\033"
CJSecurities = pd.read_csv(Path + '\\CJSecurities.csv', index_col=1, parse_dates=True)
CJSecurities = CJSecurities.iloc[:, 1:]
data0 = CJSecurities
if "openinterest" not in data0.columns:
    data0['openinterest'] = 0
data = bt.feeds.PandasData(dataname=data0)
# ---
cerebro.adddata(data)
cerebro.broker.setcash(10000.0)
# ---
class TestStrategy(bt.Strategy):
    params = ( ('maperiod', 15), )
    def __init__(self):
        self.dataclose = self.datas[0].close
        self.sma = bt.indicators.SimpleMovingAverage(self.datas[0], period=self.params.maperiod)
        self.bars_executed = 0
    def next(self):
        if not self.position:
            if self.dataclose[0] > self.sma[0]:
                self.buy()
        else:
            if len(self) >= self.bars_executed + 5:
                self.sell()
    def notify_order(self, order):
        self.bars_executed = len(self)
    def stop(self):
        print(self.params.maperiod, self.broker.getvalue())
# ------
# cerebro.addstrategy(TestStrategy) --> addstrategy() can work with run().

cerebro.optstrategy(TestStrategy,maperiod=range(5, 10)) # --> This optstrategy() get error
cerebro.run()

the error:

Process SpawnPoolWorker-4:
Traceback (most recent call last):
  File "C:\Users\i2011\AppData\Local\Programs\Python\Python37\lib\multiprocessing\process.py", line 297, in _bootstrap
    self.run()
  File "C:\Users\i2011\AppData\Local\Programs\Python\Python37\lib\multiprocessing\process.py", line 99, in run
    self._target(*self._args, **self._kwargs)
  File "C:\Users\i2011\AppData\Local\Programs\Python\Python37\lib\multiprocessing\pool.py", line 110, in worker
    task = get()
  File "C:\Users\i2011\AppData\Local\Programs\Python\Python37\lib\multiprocessing\queues.py", line 354, in get
    return _ForkingPickler.loads(res)
AttributeError: Can't get attribute 'TestStrategy' on <module '__main__' (built-in)>
Process SpawnPoolWorker-2:
Traceback (most recent call last):
  File "C:\Users\i2011\AppData\Local\Programs\Python\Python37\lib\multiprocessing\process.py", line 297, in _bootstrap
    self.run()
  File "C:\Users\i2011\AppData\Local\Programs\Python\Python37\lib\multiprocessing\process.py", line 99, in run
    self._target(*self._args, **self._kwargs)
  File "C:\Users\i2011\AppData\Local\Programs\Python\Python37\lib\multiprocessing\pool.py", line 110, in worker
    task = get()
  File "C:\Users\i2011\AppData\Local\Programs\Python\Python37\lib\multiprocessing\queues.py", line 354, in get
    return _ForkingPickler.loads(res)
AttributeError: Can't get attribute 'TestStrategy' on <module '__main__' (built-in)>
Process SpawnPoolWorker-5:
Traceback (most recent call last):
  File "C:\Users\i2011\AppData\Local\Programs\Python\Python37\lib\multiprocessing\process.py", line 297, in _bootstrap
    self.run()
  File "C:\Users\i2011\AppData\Local\Programs\Python\Python37\lib\multiprocessing\process.py", line 99, in run
    self._target(*self._args, **self._kwargs)
  File "C:\Users\i2011\AppData\Local\Programs\Python\Python37\lib\multiprocessing\pool.py", line 110, in worker
    task = get()
  File "C:\Users\i2011\AppData\Local\Programs\Python\Python37\lib\multiprocessing\queues.py", line 354, in get
    return _ForkingPickler.loads(res)
AttributeError: Can't get attribute 'TestStrategy' on <module '__main__' (built-in)>
Process SpawnPoolWorker-3:
Traceback (most recent call last):
  File "C:\Users\i2011\AppData\Local\Programs\Python\Python37\lib\multiprocessing\process.py", line 297, in _bootstrap
    self.run()
  File "C:\Users\i2011\AppData\Local\Programs\Python\Python37\lib\multiprocessing\process.py", line 99, in run
    self._target(*self._args, **self._kwargs)
  File "C:\Users\i2011\AppData\Local\Programs\Python\Python37\lib\multiprocessing\pool.py", line 110, in worker
    task = get()
  File "C:\Users\i2011\AppData\Local\Programs\Python\Python37\lib\multiprocessing\queues.py", line 354, in get
    return _ForkingPickler.loads(res)
AttributeError: Can't get attribute 'TestStrategy' on <module '__main__' (built-in)>
Process SpawnPoolWorker-1:
Traceback (most recent call last):
  File "C:\Users\i2011\AppData\Local\Programs\Python\Python37\lib\multiprocessing\process.py", line 297, in _bootstrap
    self.run()
  File "C:\Users\i2011\AppData\Local\Programs\Python\Python37\lib\multiprocessing\process.py", line 99, in run
    self._target(*self._args, **self._kwargs)
  File "C:\Users\i2011\AppData\Local\Programs\Python\Python37\lib\multiprocessing\pool.py", line 110, in worker
    task = get()
  File "C:\Users\i2011\AppData\Local\Programs\Python\Python37\lib\multiprocessing\queues.py", line 354, in get
    return _ForkingPickler.loads(res)
AttributeError: Can't get attribute 'TestStrategy' on <module '__main__' (built-in)>

I found out where the error is：
matplotlib's backend must set to "TkAgg".

cerebro.plot(iplot= True) will set backend to "nbAgg".

I want to use Backtrader on Python IDE ,not with anaconda, not in jupyter.
every is ok, only cerebro.plot() get error.
It raise : AttributeError: 'NoneType' object has no attribute 'session'.
how to solve it ?