在python中的pow（x，y，z）和x ** y％z速度的模糊性3.哪一个是有效的？

Question

结果与预期不符。 pow（x，y，z）必须高效，但结果会改变。为什么呢？

import timeit
print(timeit.timeit("pow(2505626,1520321,2700643)"))
output:3.700144177302718
print(timeit.timeit("pow(2505626,1520321,2700643)",number=1000000))
output:4.591832527890801
print(timeit.timeit("2505626**1520321%2700643",number=1000000))
output:0.014752348884940147

Answer 1

确实pow()在整数上没有很好的表现（在三个参数形式中）。请参阅函数的docstring：

代码：

def pow(*args, **kwargs): # real signature unknown
    """
    Equivalent to x**y (with two arguments) or x**y % z (with three arguments)

    Some types, such as ints, are able to use a more efficient algorithm when
    invoked using the three argument form.
    """
    pass