I'm trying to access the opening price for the current day using a custom factor (in the example below to include symbols that open over $500). It seems to work however with a one day offset (i.e. the result for a given day is actually the previous day's opening price). Any suggestions? Thanks!

from quantopian.algorithm import attach_pipeline, pipeline_output, calendars  
from quantopian.pipeline import Pipeline, CustomFactor  
from quantopian.pipeline.data.builtin import USEquityPricing

class openPrice(CustomFactor):  
    inputs = [USEquityPricing.open]  
    window_length=1  
    def compute(self, today, asset_ids, out, opens):  
        out[:] = opens[0]  


def initialize(context):  
    schedule_function(  
        func=after_trading_end,  
        date_rule = date_rules.every_day(),  
        time_rule = time_rules.market_close(),  
        calendar=calendars.US_EQUITIES,  
        half_days = True  
        )

    # Create and attach an empty Pipeline.  
    pipe = Pipeline()  
    pipe = attach_pipeline(pipe, name='my_pipeline')  
    # Construct Factors.  
    opening = openPrice()

    # Construct a Filter.  
    open_over_500 = (opening > 500)

    # Register outputs.  
    pipe.add(opening,"opening")

    # Remove rows for which the Filter returns False.  
    pipe.set_screen(open_over_500)  


def after_trading_end(context, data):  
    # Access results using the name passed to `attach_pipeline`.  
    results = pipeline_output('my_pipeline')  
    if results.empty == False:  
        print results.head(5)

    # Store pipeline results for use by the rest of the algorithm.  
    context.pipeline_results = results