Python 加减乘除左右移求幂运算符耗时对比（一清二楚）

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本文依次统计了Python3.5中

赋值=   加+   连加+=   减-   乘*   幂**   除/   整数除法//   先除再强制转换为整型 int(/)   取余%   右移>>   左移<<   取反=-

这十余种运算方式重复执行1000W次的耗时。（运行结果和结论在文章最下方）

代码如下：

from time import *iters = 10000000  # 1000w
x = 123456start_time = time()
for i in range(iters):tmp = i
end_time = time()
print('Assign = : ' + str((end_time - start_time) * 1000) + ' ms')start_time = time()
for i in range(iters):tmp = x + i# x = x + i
end_time = time()
print('Add + : ' + str((end_time - start_time) * 1000) + ' ms')tmp = 0
start_time = time()
for i in range(iters):tmp += i
end_time = time()
print('Serial add += : ' + str((end_time - start_time) * 1000) + ' ms')start_time = time()
for i in range(iters):tmp = x - i
end_time = time()
print('Sub - : ' + str((end_time - start_time) * 1000) + ' ms')start_time = time()
for i in range(iters):tmp = x * i
end_time = time()
print('Multi * : ' + str((end_time - start_time) * 1000) + ' ms')start_time = time()
for i in range(iters):tmp = x ** 2
end_time = time()
print('Pow **2 : ' + str((end_time - start_time) * 1000) + ' ms')start_time = time()
for i in range(iters):tmp = x ** 8
end_time = time()
print('Pow **8 : ' + str((end_time - start_time) * 1000) + ' ms')start_time = time()
for i in range(iters):tmp = pow(x, 2)
end_time = time()
print('pow(x, 2) : ' + str((end_time - start_time) * 1000) + ' ms')start_time = time()
for i in range(iters):tmp = pow(x, 8)
end_time = time()
print('pow(x, 8) : ' + str((end_time - start_time) * 1000) + ' ms')start_time = time()
for i in range(1, iters+1):tmp = x / i
end_time = time()
print('Div / : ' + str((end_time - start_time) * 1000) + ' ms')start_time = time()
for i in range(1, iters+1):tmp = x // i
end_time = time()
print('Int div // : ' + str((end_time - start_time) * 1000) + ' ms')start_time = time()
for i in range(1, iters+1):tmp = int(x / i)
end_time = time()
print('Div and Int() int(/) : ' + str((end_time - start_time) * 1000) + ' ms')start_time = time()
for i in range(1, iters+1):tmp = x % i
end_time = time()
print('Mod % : ' + str((end_time - start_time) * 1000) + ' ms')start_time = time()
for i in range(iters):tmp = x >> 1
end_time = time()
print('Right shift >> : ' + str((end_time - start_time) * 1000) + ' ms')start_time = time()
for i in range(iters):tmp = x << 1
end_time = time()
print('Left shift << : ' + str((end_time - start_time) * 1000) + ' ms')tmp = 1
start_time = time()
for i in range(iters):tmp = -tmp
end_time = time()
print('Neg =- : ' + str((end_time - start_time) * 1000) + ' ms')

两次运行结果：

其一：

其二：

结论：

• python中，加减乘除左右移执行时间相差不大
• 用x=-x的取反操作远远快于x*=-1
• 用x*x的乘法求平方远快于x**2，**求幂操作会随着幂指数的增加而增加耗时
• pow(x, y)略慢于x**y
• 类型转换比较耗时

环境：

python3.5

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