在python中反转字符串的最快方法
我想出了两种不同的方法来反转 Python 中的字符串.
I was able to come up with two different ways to reverse a string in Python.
常识表明，代码行数越多，运行速度就越慢.
Commonsense dictates that the more lines of code the slower it runs.
我做了以下几行代码:
代码1
"".join(reversed(map(lambda x:x,st)))
代码 2
st[::-1]
这些提供了类似的性能.对于一个 20000 长的字符串，我什至看不到性能上的差异.
These give similar performance. For a 20000 long string I am not able to see a difference of even a millisecond in performance.
我认为第一个应该是一种较慢的方法，因为它执行的操作多 3 倍.
I think the first one should be a slower approach because it performs 3x more operations.
问题
为什么我没有看到性能差异?
Why am I not seeing a performance difference?
我看到了不同之处.
首先，map(lambda x: x, st) 是怎么回事?目的是什么?
First of all, what is up with map(lambda x: x, st)? What is the purpose?
使用 timeit 模块来测试您的代码:
Use the timeit module to test your code:
$ python -m timeit '"".join(reversed("abcdefghijklmnopqrstuvwxyz"))'
1000000 loops, best of 3: 0.586 usec per loop
$ python -m timeit '"abcdefghijklmnopqrstuvwxyz"[::-1]'
10000000 loops, best of 3: 0.0715 usec per loop
如您所见，对于此特定输入，切片在我的机器上快了约 8 倍.也更简洁.
As you can see, the slice is ~8x faster on my machine for this particular input. It's also more concise.