import time

def performance(f):

    def fn(*args,**kw):

        t1=time.time()

        r=f(*args,**kw)

        t2=time.time()

        print 'call '+f.__name__+'()'+in,str(t2-t1)+'s'

        return f(*args,**kw)

    return fn

@performance

def factorial(n):

    return reduce(lambda x,y: x*y, range(1, n+1))

print factorial(10)

为什么我的输出是0.0s呢 t1-t2 应该用什么类型呢