Hi Kalin,

This is actually covered in the Pipeline Tutorial. It shows you how to dynamically select a trading universe every day by combining factors, filters and classifiers. By the end, you will construct a Mean Reversion strategy with a dynamic universe.

I hope this helps.

Hi Ernesto,
Thank you for your help.
May be I have to be more specific.
Now I have this static list of 5 securities.

 context.security_list = [sid(5061), sid(7792), sid(1941), sid(24556), sid(1746)]  

My algo is doing well with these 5 (rather arbitrary) securities, but I need to work with larger set of securities.

So, I would like to apply the Q1500US filter and to have the dynamic list of these 1500 securities which passed trough.

So which is the function (I suppose some very simple, built-in one) which I have to plug in to the pipeline (I suppose), which will provide me with this list.

Thanks a lot!

Yeah, just use Q1500US as the screen for pipeline. Check out the pipeline tutorial. Actually, the default template for new algorithms already has precisely this functionality. Each day the updated list of securities is placed into context.security_list

"""
This is a template algorithm on Quantopian for you to adapt and fill in.  
"""
from quantopian.algorithm import attach_pipeline, pipeline_output  
from quantopian.pipeline import Pipeline  
from quantopian.pipeline.data.builtin import USEquityPricing  
from quantopian.pipeline.factors import AverageDollarVolume  
from quantopian.pipeline.filters.morningstar import Q1500US  
def initialize(context):  
    """  
    Called once at the start of the algorithm.  
    """  
    # Rebalance every day, 1 hour after market open.  
    schedule_function(my_rebalance, date_rules.every_day(), time_rules.market_open(hours=1))  
    # Record tracking variables at the end of each day.  
    schedule_function(my_record_vars, date_rules.every_day(), time_rules.market_close())  
    # Create our dynamic stock selector.  
    attach_pipeline(make_pipeline(), 'my_pipeline')  
def make_pipeline():  
    """  
    A function to create our dynamic stock selector (pipeline). Documentation on  
    pipeline can be found here: https://www.quantopian.com/help#pipeline-title  
    """  
    # Base universe set to the Q500US  
    base_universe = Q1500US()

    # Factor of yesterday's close price.  
    yesterday_close = USEquityPricing.close.latest  
    pipe = Pipeline(  
        screen = base_universe,  
        columns = {  
            'close': yesterday_close,  
        }  
    )  
    return pipe  
def before_trading_start(context, data):  
    """  
    Called every day before market open.  
    """  
    context.output = pipeline_output('my_pipeline')  
    # These are the securities that we are interested in trading each day.  
    context.security_list = context.output.index  
def my_assign_weights(context, data):  
    """  
    Assign weights to securities that we want to order.  
    """  
    pass  
def my_rebalance(context,data):  
    """  
    Execute orders according to our schedule_function() timing.  
    """  
    pass  
def my_record_vars(context, data):  
    """  
    Plot variables at the end of each day.  
    """  
    pass  
def handle_data(context,data):  
    """  
    Called every minute.  
    """  
    pass

Thanks guys!
My precious algo works now! .. And we are at the next level - it performs worse.

Actually when I used these 5 securities:

 [sid(5061), sid(7792), sid(1941), sid(24556), sid(1746)]  

for the last two years it was providing positive returns well above the market (Beta 0.01, Sharpe 0.71, Returns +30.5%)

Now, with both Q1500US and Q500US (again over the last two years) it is far below the market with negative returns. (-21% returns, Beta -0.01).

I use
data.history(context.security_list, 'price', context.num_days, '1d')

Any ideas why? Too many securities?