为什么如果真比，如果1慢？ [英] Why is if True slower than if 1?

问题描述

为什么如果真比慢，如果1 在Python？不应该如果真比更快，如果1 ？

Why is if True slower than if 1 in Python? Shouldn't if True be faster than if 1?

我是想学习 timeit 模块。从最基本的开始，我想这些：

I was trying to learn the timeit module. Starting with the basics, I tried these:

>>> def test1():
...     if True:
...         return 1
...     else:
...         return 0

>>> print timeit("test1()", setup = "from __main__ import test1")
0.193144083023


>>> def test2():
...     if 1:
...         return 1
...     else:
...         return 0

>>> print timeit("test2()", setup = "from __main__ import test2")
0.162086009979


>>> def test3():
...     if True:
...             return True
...     else:
...             return False

>>> print timeit("test3()", setup = "from __main__ import test3")
0.214574098587

>>> def test4():
...     if 1:
...             return True
...     else:
...             return False

>>> print timeit("test4()", setup = "from __main__ import test4")
0.160849094391

我对这些事情感到困惑：

I am confused by these things:

1. 据西尔Defresne先生在回应<一个href=\"http://stackoverflow.com/questions/100732/why-is-if-not-someobj-better-than-if-someobj-none-in-python\">this问题，一切都隐式转换为布尔，然后再检查。那么，为什么是如果真比慢，如果1 ？


2. 为什么 TEST3 比测试1 即使只有收益值是不同的？


3. 就像第二个问题，但为什么是 TEST4 一点点的更快的比测试2 ？

1. According to the response from Mr. Sylvain Defresne in this question, everything is implicitly converted to a bool first and then checked. So why is if True slower than if 1?
2. Why is test3 slower than test1 even though only the return values are different?
3. Like Question 2, but why is test4 a little faster than test2?

请注意：我跑了 timeit 三次，拿着结果的平均值，然后贴在这里的时间与code沿

NOTE: I ran timeit three times and took the average of the results, then posted the times here along with the code.

这个问题并不涉及到如何做微基准测试（我没有在这个例子中，但我也明白，这是太简单了），但为什么检查真变量大于一个常数慢。

This question does not relate to how to do micro benchmarking(which I did in this example but I also understand that it is too basic) but why checking a 'True' variable is slower than a constant.

推荐答案

真和假不是关键字的Python 2 。

他们必须在运行时解决。这在 Python中被改变3

They must resolve at runtime. This has been changed in Python 3

在Python 3的相同的测试：

Same test on Python 3:

>>> timeit.timeit('test1()',setup="from __main__ import test1", number=10000000)
2.806439919999889
>>> timeit.timeit('test2()',setup="from __main__ import test2", number=10000000)
2.801301520000038
>>> timeit.timeit('test3()',setup="from __main__ import test3", number=10000000)
2.7952816800000164
>>> timeit.timeit('test4()',setup="from __main__ import test4", number=10000000)
2.7862537199999906

时间误差是1％，这是可以接受的。

Time error is in 1%, which is acceptable.

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