范围(len(list))还是枚举(list)?
问题描述
可能重复:
只需要索引:枚举或(x)范围?
哪些会被认为更好/更清晰/更快/更Pythonic"?我不关心列表L的内容，只关心它有多长.
Which of these would be considered better/clearer/faster/more 'Pythonic'? I don't care about the content of the list L, just how long it is.
a = [f(n) for n, _ in enumerate(L)]
或
a = [f(n) for n in range(len(L))]
如果有什么不同，f 函数也会使用 len(list).
If it makes any difference, the function f makes use of len(list) as well.
解决方案
一些快速的计时运行似乎给使用 range() 的第二个选项比 enumerate():
Some quick timing runs seem to give the 2nd option using range() a slight edge over enumerate():
timeit a = [f(n) for n, _ in enumerate(mlist)]
10000 loops, best of 3: 118 us per loop
timeit a = [f(n) for n in range(len(mlist))]
10000 loops, best of 3: 102 us per loop
只是为了好玩，使用 xrange() (Python v2.7.2)
and just for fun using xrange() (Python v2.7.2)
timeit a = [f(n) for n in xrange(len(mlist))]
10000 loops, best of 3: 99 us per loop
我倾向于首先使用可读代码，然后使用 xrange()(如果可用)(即 Pre-Python v 3.x)，然后是 range() 和 enumerate().
I would favor readable code first, then using xrange() if available (i.e., Pre-Python v 3.x), followed by range() and enumerate().
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