python - Python 可以让列表更高效吗？

Question

在 Python v2.7 中，如果我有这样的函数:

def holes_between(intervals):
  # Compute the holes between the intervals, for example:
  #   given the intervals: ([ 8,  9] [14, 18] [19, 20] [23, 32] [34, 49])
  #     compute the holes: ([10, 13] [21, 22] [33, 33])
  prec = intervals[0][1] + 1 # Bootstrap the iteration
  for low, high in intervals[1:]:
    if prec <= low - 1:
      yield (prec, low - 1)
    prec = high + 1

holes = list(holes_between(intervals))

由于函数的 yield 被收集到 list 中，在 holes_between 函数中构建列表是否更有效如果是这样，如何最有效地做到这一点？

Answer 1

与直接构建列表相比，生成器函数可能效率较低。

您可以在 holes_between() 函数中构建列表并返回:

def holes_between(intervals):
    prec = intervals[0][1] + 1 # Bootstrap the iteration
    result = []
    for low, high in intervals[1:]:
        if prec <= low - 1:
            result.append((prec, low - 1))
        prec = high + 1
    return result

但要测量差异，使用 timeit module .

如果您有一些典型的输入，您可以使用以下方法进行测试:

import timeit

def holes_between_list(intervals):
    prec = intervals[0][1] + 1 # Bootstrap the iteration
    result = []
    for low, high in intervals[1:]:
        if prec <= low - 1:
            result.append((prec, low - 1))
        prec = high + 1
    return result

def holes_between_generate(intervals):
    prec = intervals[0][1] + 1 # Bootstrap the iteration
    for low, high in intervals[1:]:
        if prec <= low - 1:
            yield (prec, low - 1)
        prec = high + 1

intervals = [ ... ] # fill in some test data

print 'As list:', timeit.timeit(
    'holes_between(intervals)',
    'from __main__ import intervals, holes_between_list as holes_between')

print 'Using a generator:', timeit.timeit(
    'list(holes_between(intervals))',
    'from __main__ import intervals, holes_between_generate as holes_between')

值越小，测试数据的方法越快。