在Python中快速將bytearray轉換為元組數組（不使用NumPy）

Question

我需要加快以下代碼： -

index = 0
WIDTH = 1920
HEIGHT = 1080
for o in xrange(WIDTH * HEIGHT):
    outbuf[o] = (buffer[index], buffer[index+1], buffer[index+2])
    index += 3

這將bytearray轉換為元組數組，但速度太慢，有沒有辦法讓它更快，而不使用numpy。

Answer 1

使用itertools的石斑魚配方構建outbuf的速度幾乎是我機器的兩倍。

這是文檔中的分組函數：

def grouper(iterable, n, fillvalue=None):
    "Collect data into fixed-length chunks or blocks"
    # grouper('ABCDEFG', 3, 'x') --> ABC DEF Gxx
    args = [iter(iterable)] * n
    return izip_longest(fillvalue=fillvalue, *args)

這個腳本比較問題中函數的時間，使用石斑魚填充outbuf並使用石斑魚返回outbuf而不是填充外部列表。 最快的方法是從函數返回outbuf 。

from itertools import izip_longest
import random
import sys
import timeit

WIDTH = 1920
HEIGHT = 1080


buffer_ = bytearray(random.randint(0, 255) for _ in xrange(WIDTH * HEIGHT * 3))

# Function from the question
def extract(buffer_):
    index = 0
    for o in xrange(WIDTH * HEIGHT):
        outbuf[o] = (buffer_[index], buffer_[index+1], buffer_[index+2])
        index += 3


def grouper(iterable, n, fillvalue=None):
    args = [iter(iterable)] * n
    return izip_longest(fillvalue=fillvalue, *args)


# Use grouper with external outbuf
def grouper_extract(buffer_):
    groups = grouper(buffer_, 3)
    for o in xrange(WIDTH * HEIGHT):
        outbuf[o] = next(groups)


# Return a list using grouper
def grouper_list(buffer_):
    return list(grouper(buffer_, 3))


if __name__ == '__main__':
    # Set number of timeit repetitions.
    try:
        number = int(sys.argv[1])
    except IndexError:
        number = 50
    outbuf = [0 for _ in xrange(WIDTH * HEIGHT * 3)]
    print 'OP function'
    print timeit.timeit(setup="from __main__ import extract, outbuf, buffer_",
                        stmt="extract(buffer_)", number=number)
    print
    print 'Fill external outbuf with grouper'
    print timeit.timeit(setup="from __main__ import grouper_extract, outbuf, buffer_",
                        stmt="grouper_extract(buffer_)", number=number)
    print
    print 'Return outbuf using grouper'
    print timeit.timeit(setup="from __main__ import grouper_list, buffer_",
                        stmt="outbuf = grouper_list(buffer_)", number=number)
    print

以下是每種方法重復50次的時間：

OP function
39.3345730305

Fill external outbuf with grouper
30.0249710083

Return outbuf using grouper
20.357350111