将一个整数转换为浮点数的原因是什么慢于在Python中为该int添加0.0？
import timeit
def add_simple():
for i in range(1000):
a = 1 + 0.0
def cast_simple():
for i in range(1000):
a = float(1)
def add_total():
total = 0
for i in range(1000):
total += 1 + 0.0
def cast_total():
total = 0
for i in range(1000):
total += float(1)
print "Add simple timing: %s" % timeit.timeit(add_simple,number=1)
print "Cast simple timing: %s" % timeit.timeit(cast_simple,number=1)
print "Add total timing: %s" % timeit.timeit(add_total,number=1)
print "Cast total timing: %s" % timeit.timeit(cast_total,number=1)
其输出为：
Add simple timing: 0.0001220703125
Cast simple timing: 0.000469923019409
Add total timing: 0.000164985656738
Cast total timing: 0.00040078163147
解决方法
如果您使用dis模块，您可以开始看到为什么：
In [11]: dis.dis(add_simple)
2 0 SETUP_LOOP 26 (to 29)
3 LOAD_GLOBAL 0 (range)
6 LOAD_CONST 1 (1000)
9 CALL_FUNCTION 1 (1 positional,0 keyword pair)
12 GET_ITER
>> 13 FOR_ITER 12 (to 28)
16 STORE_FAST 0 (i)
3 19 LOAD_CONST 4 (1.0)
22 STORE_FAST 1 (a)
25 JUMP_ABSOLUTE 13
>> 28 POP_BLOCK
>> 29 LOAD_CONST 0 (None)
32 RETURN_VALUE
In [12]: dis.dis(cast_simple)
2 0 SETUP_LOOP 32 (to 35)
3 LOAD_GLOBAL 0 (range)
6 LOAD_CONST 1 (1000)
9 CALL_FUNCTION 1 (1 positional,0 keyword pair)
12 GET_ITER
>> 13 FOR_ITER 18 (to 34)
16 STORE_FAST 0 (i)
3 19 LOAD_GLOBAL 1 (float)
22 LOAD_CONST 2 (1)
25 CALL_FUNCTION 1 (1 positional,0 keyword pair)
28 STORE_FAST 1 (a)
31 JUMP_ABSOLUTE 13
>> 34 POP_BLOCK
>> 35 LOAD_CONST 0 (None)
38 RETURN_VALUE
注意CALL_FUNCTION
