Strategy - Bollinger-Bands-Single-Stock

"""
Algo to trade Johnson and Johnson using Bollinger Bands as trading signals. When the stock price rises above the upper Bollinger Band we short, when it drops below lower Bollinger Band we go long.
Johnson and Johnson can be reaplced with any stock by replacing the Stock ID (sid) below
"""

def initialize(context):
    """
    Called once at the start of the algorithm.
    """
    # Rebalance daily, at market open
    schedule_function(check_bollinger,date_rules.every_day())
    
    # save stock Johnson and Johnson as jnj
    context.jnj = sid(4151)
    

def check_bollinger(context,data):
    """
    Check if outside Bollinger Bands
    """
    
    jnj = context.jnj
    # Get current price
    current_price = data.current(jnj,'price')
    
    hist = data.history(
        jnj,
        fields='price',
        bar_count=20,
        frequency='1d'
        )
    
    # Get 20 day mean
    mavg_20 = hist.mean()
    
    # Get 20 day standard deviation
    msd_20 = hist.std()
    
    # Create upper and lower bands
    upper_band = mavg_20 + 2 * msd_20
    lower_band = mavg_20 - 2 * msd_20
    
    # Short, long or stick?
    if current_price <= lower_band:
        order_target_percent(jnj,1.0)
        print("I'm going long!")
    elif current_price >= upper_band:
        order_target_percent(jnj,-1.0)
        print("Short it baby!")