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Adapting an algorithm from working with one stock to working with many.

Hello,
I am trying to adapt this algorithm from working with only one stock to working with either one stock or many stocks but cannot figure out exactly how to accomplish this. Thanks for the help. Here is the code for the one stock only version:

# Put any initialization logic here.  The context object will be passed to  
# the other methods in your algorithm.  
def initialize(context):  
    context.security = sid(20541)

# Will be called on every trade event for the securities you specify.  
def handle_data(context, data):  
    print(data)  
    MA1 = data[context.security].mavg(50)  
    MA2 = data[context.security].mavg(100)  
    current_price = data[context.security].price  
    current_positions = context.portfolio.positions[context.security].amount  
    cash = context.portfolio.cash  
    if (MA1 > MA2) and current_positions == 0:  
        number_of_shares = int(cash/current_price)  
        order(context.security, number_of_shares)  
        log.info("buying shares")  
    elif (MA1 < MA2) and current_positions != 0:  
        order_target(context.security, 0)  
        log.info("selling shares")  
    record(MA1 = MA1, MA2 = MA2, Price = current_price)  

Thanks,
Nick

3 responses

Hey Nick,
I shared a pattern for doing this sort of thing in this post a while back. Factoring the single stock strategy into a class is a good way to go because you don't have to change much code and it allows you to create several instances with different stocks/parameters.

David

So I figured out how to change the code to work with multiple sids (not the way above though). But now I cannot use just one sid. If I do this I get a runtime error on line 22 (see the backtest). I'm not sure if the error is visible on the backtest without running the code. The error says:
There was a runtime error.
TypeError: 'zipline.assets._assets.Equity' object is not iterable
User Algorithm: 22, in handleData
for stock in context.stocks:

Please note that handleData is not the same as handle_data. Does anyone know where I have gone wrong?

Thanks,
Nick

Nick, I think putting the sid in brackets solves the problem:

context.stocks = [sid(24)]  

Now you have a list of one item, which is iterable!

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