from matplotlib.finance import quotes_historical_yahoo
import numpy as np
import pandas as pd
ticker='IBM'
begdate=(1990,1,1)
enddate=(2012,12,31)
x=quotes_historical_yahoo(ticker,begdate,enddate,asobject=True,adjusted=True)
logret = log(x.aclose[1:]/x.aclose[:-1])
date=[]
d0=x.date
for i in range(0,size(logret)):
date.append(d0[i].strftime("%Y"))
y=pd.DataFrame(logret,date,columns=['ret_annual'])
ret_annual=exp(y.groupby(y.index).sum())-1