Missing price info for quite a few NSE Symbols

AI & Machine learning
1

On trying to backtest on certain stock symbols i am getting no price data. For eg. ran the below code for 2 symbols  - 'EROSMEDIA','ARSSINFRA' which are around since 2019. The backtest starts from Jan 2022 (2022-01-03) using the below code i am getting nan as price for the most recent date for EROSMEDIA and no price at all for ARSSINFRA, why would that be ?

 

CODE -

context.securities = [symbol('EROSMEDIA'), sumbol('ARSSINFRA')]
price_data = data.history(context.securities, 'close',201,'1d')
for security in context.securities:
        px = price_data.loc[:,security].values
        print(security,px[-1],px[-2],px[-100],px[-200],px[1],px[2])


Output
datetime 2022-01-03 09:45:00+05:30
inside generate_signals
Equity(EROSMEDIA [250]) nan nan 21.35 30.25 30.25 29.7
Equity(ARSSINFRA [61]) nan nan nan nan nan nan
2

On Blueshift, we follow a liquidity (+ penny stock) filtered universe to ensure an universe which is survivorship bias free and suitable for quant analysis and strategies. The examples above are stocks that fell out of the universe at some point. To see the life time of a stock, first fetch the asset (e.g. asset = symbol('ARSSINFRA')) and then check the start and the end date to see the life time of the asset in the universe (e.g. asset.start_date). Data query for an asset will return data only for the available period. Similarly, backtesting will allow trading in those assets only during the lifetime of the asset.