import numpy as np
def annualized_sharpe(returns, N=252):
""" Calculate annualized Sharpe ratio of a returns stream
based on number of trading periods in a year (N).
Args:
returns (pandas.Series): daily (or other) returns on investment
N (int): number of periods in a year
Returns:
float: Sharpe ratio
"""
return np.sqrt(N) * returns.mean() / returns.std()