Hello,

First, I really love this framework. I've learned a lot just reading the documentation and source code and I find it great to work with. It's really a thoughtful and well executed project.

I have a question on general architecture and more specifically datafeeds.

I would like to apply a single strategy on several commodities markets and get performance data on this strategy at a portfolio level. I've seen one discussion on this:

https://community.backtrader.com/topic/9/portfolio-inventory-management/2

That's fairly clear (at least before working on it directly I understand the concept), but in relation to data feeds and contract rolling I was wondering how best to handle the situation.

From what I understand from the documentation rolling futures involves entering all contracts as independent data feeds and these data feeds are given as input to bt.feeds.RollOver (for quick reference: https://www.backtrader.com/docu/data-rollover/rolling-futures-over.html).

My question is this -- if I want to do a test across WTI for example from 1995 to 2010 I have 180 data feeds to enter (12 * 15). Then if I want to test the portfolio across 25 products I get into the thousands of feeds quite quickly. Am I correct in my understanding?

Another option is completing the rolling operations externally, storing this data in a csv and using a rolled csv as a data feed. This is how I currently use the system but it becomes problematic when I do operations on a look back window, for example. I need to do operations externally of backtrader. I would prefer to keep the strategy implementation fully inside back trader.

I have a function that takes a datetime object as a parameter and returns a list of the front, first roll, second roll etc for the given date, among other information. I was wondering if it was possible to provide a function as input to a data feed such that the data feed provided to the Strategy object is in essence a symbol and a rolling function (in other words, it doesn't yet hold data but knows what to do when the strategy iteratively provides it a date during the implementation of the strategy.

Hopefully this makes sense -- any thoughts or ideas would be greatly appreciated.