import pandas as pd
from pandas_datareader import data as web
import numpy as np

tickers={'stock':['AAPL', 'GOOGL', 'TSLA'], 'quantity': [50, 100,300]}
df=pd.DataFrame(tickers)
stock_prices=web.DataReader(['AAPL', 'GOOGL', 'TSLA'], data_source='yahoo', start='2017-01-01', end='2020-01-01')['Close']
#add an empy column

#stock_prices["Ptf_Value"] = ""
def ValuePortfolio():
    stock_prices['Ptf_Value'] = 0
    i=0
    while i<= len(tickers):
        stock = tickers['stock'][i]
        quantity = tickers['quantity'][i]
        stock_prices['Ptf_Value']  = stock_prices * quantity + stock_prices['Ptf_Value']
        i = i+1

ValuePortfolio()