First, define this list of stocks which we will be using later.

stocks = ['MMM', 'ABT', 'ABBV', 'ACN', 'ATVI', 'AYI', 'ADBE', 'AMD', 'AAP', 'AES', 'AET', 'AMG', 'AFL', 'A', 'APD', 'AKAM', 'ALK', 'ALB', 'ARE', 'ALXN', 'ALLE', 'AGN', 'ADS', 'LNT', 'ALL', 'GOOGL', 'GOOG', 'MO', 'AMZN', 'AEE', 'AAL', 'AEP', 'AXP', 'AIG', 'AMT', 'AWK', 'AMP', 'ABC', 'AME', 'AMGN', 'APH', 'APC', 'ADI', 'ANTM', 'AON', 'APA', 'AIV', 'AAPL', 'AMAT', 'ADM', 'ARNC', 'AJG', 'AIZ', 'T', 'ADSK', 'ADP', 'AN', 'AZO', 'AVB', 'AVY', 'BHI', 'BLL', 'BAC', 'BK', 'BCR', 'BAX', 'BBT', 'BDX', 'BBBY', 'BRK.B', 'BBY', 'BIIB', 'BLK', 'HRB', 'BA', 'BWA', 'BXP', 'BSX', 'BMY', 'AVGO', 'BF.B', 'CHRW', 'CA', 'COG', 'CPB', 'COF', 'CAH', 'CBOE', 'KMX', 'CCL', 'CAT', 'CBG', 'CBS', 'CELG', 'CNC', 'CNP', 'CTL', 'CERN', 'CF', 'SCHW', 'CHTR', 'CHK', 'CVX', 'CMG', 'CB', 'CHD', 'CI', 'XEC', 'CINF', 'CTAS', 'CSCO', 'C', 'CFG', 'CTXS', 'CLX', 'CME', 'CMS', 'COH', 'KO', 'CTSH', 'CL', 'CMCSA', 'CMA', 'CAG', 'CXO', 'COP', 'ED', 'STZ', 'COO', 'GLW', 'COST', 'COTY', 'CCI', 'CSRA', 'CSX', 'CMI', 'CVS', 'DHI', 'DHR', 'DRI', 'DVA', 'DE', 'DLPH', 'DAL', 'XRAY', 'DVN', 'DLR', 'DFS', 'DISCA', 'DISCK', 'DISH', 'DG', 'DLTR', 'D', 'DOV', 'DOW', 'DPS', 'DTE', 'DD', 'DUK', 'DXC', 'ETFC', 'EMN', 'ETN', 'EBAY', 'ECL', 'EIX', 'EW', 'EA', 'EMR', 'ETR', 'EVHC', 'EOG', 'EQT', 'EFX', 'EQIX', 'EQR', 'ESS', 'EL', 'ES', 'EXC', 'EXPE', 'EXPD', 'ESRX', 'EXR', 'XOM', 'FFIV', 'FB', 'FAST', 'FRT', 'FDX', 'FIS', 'FITB', 'FE', 'FISV', 'FLIR', 'FLS', 'FLR', 'FMC', 'FL', 'F', 'FTV', 'FBHS', 'BEN', 'FCX', 'GPS', 'GRMN', 'IT', 'GD', 'GE', 'GGP', 'GIS', 'GM', 'GPC', 'GILD', 'GPN', 'GS', 'GT', 'GWW', 'HAL', 'HBI', 'HOG', 'HRS', 'HIG', 'HAS', 'HCA', 'HCP', 'HP', 'HSIC', 'HSY', 'HES', 'HPE', 'HOLX', 'HD', 'HON', 'HRL', 'HST', 'HPQ', 'HUM', 'HBAN', 'IDXX', 'INFO', 'ITW', 'ILMN', 'IR', 'INTC', 'ICE', 'IBM', 'INCY', 'IP', 'IPG', 'IFF', 'INTU', 'ISRG', 'IVZ', 'IRM', 'JEC', 'JBHT', 'SJM', 'JNJ', 'JCI', 'JPM', 'JNPR', 'KSU', 'K', 'KEY', 'KMB', 'KIM', 'KMI', 'KLAC', 'KSS', 'KHC', 'KR', 'LB', 'LLL', 'LH', 'LRCX', 'LEG', 'LEN', 'LVLT', 'LUK', 'LLY', 'LNC', 'LKQ', 'LMT', 'L', 'LOW', 'LYB', 'MTB', 'MAC', 'M', 'MNK', 'MRO', 'MPC', 'MAR', 'MMC', 'MLM', 'MAS', 'MA', 'MAT', 'MKC', 'MCD', 'MCK', 'MJN', 'MDT', 'MRK', 'MET', 'MTD', 'KORS', 'MCHP', 'MU', 'MSFT', 'MAA', 'MHK', 'TAP', 'MDLZ', 'MON', 'MNST', 'MCO', 'MS', 'MOS', 'MSI', 'MUR', 'MYL', 'NDAQ', 'NOV', 'NAVI', 'NTAP', 'NFLX', 'NWL', 'NFX', 'NEM', 'NWSA', 'NWS', 'NEE', 'NLSN', 'NKE', 'NI', 'NBL', 'JWN', 'NSC', 'NTRS', 'NOC', 'NRG', 'NUE', 'NVDA', 'ORLY', 'OXY', 'OMC', 'OKE', 'ORCL', 'PCAR', 'PH', 'PDCO', 'PAYX', 'PYPL', 'PNR', 'PBCT', 'PEP', 'PKI', 'PRGO', 'PFE', 'PCG', 'PM', 'PSX', 'PNW', 'PXD', 'PNC', 'RL', 'PPG', 'PPL', 'PX', 'PCLN', 'PFG', 'PG', 'PGR', 'PLD', 'PRU', 'PEG', 'PSA', 'PHM', 'PVH', 'QRVO', 'PWR', 'QCOM', 'DGX', 'RRC', 'RJF', 'RTN', 'O', 'RHT', 'REG', 'REGN', 'RF', 'RSG', 'RAI', 'RHI', 'ROK', 'COL', 'ROP', 'ROST', 'RCL', 'R', 'CRM', 'SCG', 'SLB', 'SNI', 'STX', 'SEE', 'SRE', 'SHW', 'SIG', 'SPG', 'SWKS', 'SLG', 'SNA', 'SO', 'LUV', 'SPGI', 'SWK', 'SPLS', 'SBUX', 'STT', 'SRCL', 'SYK', 'STI', 'SYMC', 'SYF', 'SNPS', 'SYY', 'TROW', 'TGT', 'TEL', 'FTI', 'TDC', 'TSO', 'TXN', 'TXT', 'TMO', 'TIF', 'TWX', 'TJX', 'TMK', 'TSS', 'TSCO', 'TDG', 'RIG', 'TRV', 'TRIP', 'FOXA', 'FOX', 'TSN', 'UDR', 'ULTA', 'USB', 'UA', 'UAA', 'UNP', 'UAL', 'UNH', 'UPS', 'URI', 'UTX', 'UHS', 'UNM', 'VFC', 'VLO', 'VAR', 'VTR', 'VRSN', 'VRSK', 'VZ', 'VRTX', 'VIAB', 'V', 'VNO', 'VMC', 'WMT', 'WBA', 'DIS', 'WM', 'WAT', 'WEC', 'WFC', 'HCN', 'WDC', 'WU', 'WRK', 'WY', 'WHR', 'WFM', 'WMB', 'WLTW', 'WYN', 'WYNN', 'XEL', 'XRX', 'XLNX', 'XL', 'XYL', 'YHOO', 'YUM', 'ZBH', 'ZION', 'ZTS']

Now time to get some stock data, just for Ford.

import pandas_datareader as pdr
import datetime
start = datetime.datetime(2016, 1, 1)
end = datetime.datetime(2017, 1, 1)
stocks1 = pdr.get_data_yahoo("F",start, end)["Adj Close"]
print(stocks1)

Just like we did in the first lesson, let’s normalize the stock data.

import numpy as np
stocks1 = stocks1/stocks1.iloc[0]
print(stocks1)

Now get the variance.

stocks1 = stocks1.pct_change().dropna()
print(np.var(stocks1,ddof=1))

Something to note about this variance, it is the variance of daily returns. But what if we want to find the variance over a year (which is a lot of times what we do want). To find this, you simply multiply the variance by a factor representing how much longer you want the period to be. So if it was the variance over 5 days, multiply by 5, but for our purposes we will multiply by 252 (the number of trading days in a year). Let’s see what variance is, and then what standard deviation is.

print(np.var(stocks1,ddof=1)*252)
print((np.var(stocks1,ddof=1)*252)**.5)

When you want to convert standard deviation from one period you multiply by this same factor, except you take the square root of it.