Problem with custom ohlc vars

arrr

I'm trying to maintain code compatibility with my production environment, where I'm storing ohlc data in a dict:
self.ohlc = {-3: {'o': 153.252, 'h': 155.84, 'l': 149.49, 'c': 152.42, 'vol': 155395.333}, -2: {'o': 152.417, 'h': 162.4, 'l': 149.78, 'c': 155.65, 'vol': 255543.915}, -1: {'o': 155.7, 'h': 161.04, 'l': 150.88, 'c': 158.48, 'vol': 297664.05400000006}, 0: {'o': 158.71, 'h': 167.0, 'l': 158.51, 'c': 162.0, 'vol': 189163.71099999998}}
where self.ohlc[0]['l] is the low if the current bar and self.ohlc[-3]['h'] stands for high 3 bars ago.
I was trying to replicate the same with backtrader by doing:

    def make_ohlc(self):
        ohlc_dict = {}
        for x in range(-3, 1):
            ohlc = {'o': self.datas[0].open[x], 'h': self.datas[0].high[x], 'l': self.datas[0].low[x], 'c': self.datas[0].close[x]}
            ohlc_dict[x] = ohlc
        return ohlc_dict

and calling it from init:
self.ohlc = self.make_ohlc()
But once I do that - I'm getting weird error:

  File "/Users/arrrr/PycharmProjects/backtrader/reverse.py", line 217, in <module>
    cerebro.run()
  File "/Users/arrrr/PycharmProjects/backtrader/venv/lib/python3.6/site-packages/backtrader/cerebro.py", line 1127, in run
    runstrat = self.runstrategies(iterstrat)
  File "/Users/arrrr/PycharmProjects/backtrader/venv/lib/python3.6/site-packages/backtrader/cerebro.py", line 1217, in runstrategies
    strat = stratcls(*sargs, **skwargs)
  File "/Users/arrrr/PycharmProjects/backtrader/venv/lib/python3.6/site-packages/backtrader/metabase.py", line 88, in __call__
    _obj, args, kwargs = cls.doinit(_obj, *args, **kwargs)
  File "/Users/arrrr/PycharmProjects/backtrader/venv/lib/python3.6/site-packages/backtrader/metabase.py", line 78, in doinit
    _obj.__init__(*args, **kwargs)
  File "/Users/arrrr/PycharmProjects/backtrader/reverse.py", line 50, in __init__
    self.make_ohlc()
  File "/Users/arrrr/PycharmProjects/backtrader/reverse.py", line 55, in make_ohlc
    ohlc = {'o': self.dataopen[x], 'h': self.datahigh[x], 'l': self.datalow[x],
  File "/Users/arrrr/PycharmProjects/backtrader/venv/lib/python3.6/site-packages/backtrader/linebuffer.py", line 163, in __getitem__
    return self.array[self.idx + ago]
IndexError: array index out of range

However if I call same self.make_ohlc() from self.next() - it works (it's obvious that calling it every bar is not a proper way to handle this)
Any ideas what I'm doing wrong?

backtrader

@arrr said in Problem with custom ohlc vars:

and calling it from __init:__

__init__ is there to initialize things. Data feeds are not producing data yet.

You probably want to read:

Docs - Platform Concepts

and the lifecycle of a strategy (right at the beginning)

Docs - Strategy

backtrader

@arrr said in Problem with custom ohlc vars:

it's obvious that calling it every bar is not a proper way to handle this

I missed that before. The question is: why?

backtrader isn't pandas (which many people apparently believe). Evaluation of things happens with each new incoming tick, which is given to the user during next, where you have access to the data.

arrr

@backtrader this gonna work fine, considering I'm using data replay?

backtrader

@arrr said in Problem with custom ohlc vars:

this gonna work fine, considering I'm using data replay?

What should work fine? The info you have provided in this thread is close to none. You simply say that you cannot get data in __init__, which is something obvious.

arrr

@backtrader said in Problem with custom ohlc vars:

@arrr said in Problem with custom ohlc vars:

this gonna work fine, considering I'm using data replay?

What should work fine? The info you have provided in this thread is close to none. You simply say that you cannot get data in __init__, which is something obvious.

I mean calling self.make_ohlc() on every next() and operating what it returns as ohlc data

backtrader

@arrr said in Problem with custom ohlc vars:

However if I call same self.make_ohlc() from self.next() - it works

I fail to understand what the problem is. You have for sure a very clear idea about what troubles you, but you have already said it works. What you want to do with the data is of course unknown.

arrr

@backtrader said in Problem with custom ohlc vars:

@arrr said in Problem with custom ohlc vars:

However if I call same self.make_ohlc() from self.next() - it works

I fail to understand what the problem is. You have for sure a very clear idea about what troubles you, but you have already said it works. What you want to do with the data is of course unknown.

Sorry for confusing explanation. It technically works, but I did not check if it returns correct data and, as for me, the code looks pretty weird :)