Python整数除法运算符vs math.floor

Question

使用整数除法运算符比math.floor有什么好处吗？

7 // 2 

在

math.floor(7/2) 

Answer 1

Integer div ision比math.floor函数调用更快：

>>> import timeit 
>>> timeit.timeit('7//2') 
0.024671780910702337 
>>> timeit.timeit('floor(7/2)', setup='from math import floor') 
0.27053647879827736 
>>> timeit.timeit('math.floor(7/2)', setup='import math') 
0.3131167508719699 

正如你可以用这个拆卸看到，使用math模块的floor函数（import math和math.floor或from math import floor和floor）涉及额外的查找和函数调用在平原整数除法：

>>> import dis 
>>> import math 
>>> from math import floor 
>>> def integer_division(): 
...  7//2 
... 
>>> def math_floor(): 
...  floor(7/2) 
... 
>>> def math_full_floor(): 
...  math.floor(7/2) 
... 
>>> dis.dis(integer_division) 
    2   0 LOAD_CONST    3 (3) 
       3 POP_TOP 
       4 LOAD_CONST    0 (None) 
       7 RETURN_VALUE 
>>> dis.dis(math_floor) 
    2   0 LOAD_GLOBAL    0 (floor) 
       3 LOAD_CONST    3 (3.5) 
       6 CALL_FUNCTION   1 (1 positional, 0 keyword pair) 
       9 POP_TOP 
      10 LOAD_CONST    0 (None) 
      13 RETURN_VALUE 
>>> dis.dis(math_full_floor) 
    2   0 LOAD_GLOBAL    0 (math) 
       3 LOAD_ATTR    1 (floor) 
       6 LOAD_CONST    3 (3.5) 
       9 CALL_FUNCTION   1 (1 positional, 0 keyword pair) 
      12 POP_TOP 
      13 LOAD_CONST    0 (None) 
      16 RETURN_VALUE 

Answer 2

当然，还有在函数调用一些开销，如果你这样做足够的时间，你看到的速度差：

Run time for //: 12.940021991729736 sec 
Run time for floor: 26.933987855911255 sec 

下面的代码我跑了：

from time import time 
from math import floor 

start_time = time() 
for i in range(1, 10000): 
    for j in range(1, 10000): 
     result = i // j 
print('Run time for //:', time() - start_time, 'sec') 

start_time = time() 
for i in range(1, 10000): 
    for j in range(1, 10000): 
     result = floor(i/j) 
print('Run time for floor:', time() - start_time, 'sec')