import time

def performance(unit):
    def perf_decorator(f):
        def wrapper(*args, **kw):
            t1 = time.time()
            r = f(*args, **kw)
            t2 = time.time()
            t = (t2 - t1)*1000 if unit =='ms' else (t2 - t1)
            print 'call %s() in %f %s'%(f.__name__, t, unit)
            return r
        return wrapper
    return perf_decorator

@performance('ms')  
def factorial(n):
    return reduce(lambda x,y: x*y, range(1, n+1))

print factorial(10)