Sizer calculating ATR indicator values

Is there a way for a sizer to hold the ATR calculation without initializing ATR in the strategy init?
For design decoupling purposes I would like the sizer to calculate a specific ticker's ATR value and then compute the position size,the ATR calculation should be the sizer's "head ache",not the strategies init ..
Can a sizer calculate ATR values for data without that ATR been initialized in the strategy?this does not seem to calculate ATR values :
# inside the sizer def _getsizing(self, comminfo, cash, data, isbuy): atr = bt.indicators.ATR(data, period=self.atr_parameter) # not initialized in __init__,**always empty ...** return position_size_that_depends_on_atr # crash ..

The
Sizer
instance is created inside the Strategy and the indicator will look for such Strategy to register itself. It has to do it or it wouldn't else work.Bottomline: It will still be as if you had done inside the Strategy
Caveat Emptor: never tried.

OK,
Thank you for your reply ( and kudos on the incredible work ..) 
Has this been solved? If so is it possible to post the Sizer code? Thanks!

class AtrBasedPositionSize(bt.Sizer): def __init__(self, atr_parameter, one_bar_risk, atrs): self.atr_parameter = atr_parameter self.atrs = atrs def _getsizing(self, comminfo, cash, data, isbuy): if(len(data)<=self.atr_parameter):return 0 ticker = data._name position_size = int((self.broker.getvalue()) / self.atrs[ticker][0]) return position_size

Thanks !