python：有一个库函数用于分块输入流吗？ [英] python: is there a library function for chunking an input stream?

问题描述

我想对输入流进行分块以进行批处理。给定输入列表或生成器，

I want to chunk an input stream for batch processing. Given an input list or generator,

x_in = [1, 2, 3, 4, 5, 6 ...]

我想要一个函数，该函数将返回该输入的大块。假设，如果 chunk_size = 4 ，则

I want a function that will return chunks of that input. Say, if chunk_size=4, then,

x_chunked = [[1, 2, 3, 4], [5, 6, ...], ...]

这是我一遍又一遍的事情，我想知道是否有比我自己编写的方法更标准的方法。我在 itertools 中缺少什么吗？ （一个人可以用 enumerate 和 groupby 解决该问题，但这感觉很笨拙。）万一有人想看到一个

This is something I do over and over, and was wondering if there is a more standard way than writing it myself. Am I missing something in itertools? (One could solve the problem with enumerate and groupby, but that feels clunky.) In case anyone wants to see an implementation, here it is,

def chunk_input_stream(input_stream, chunk_size):
    """partition a generator in a streaming fashion"""
    assert chunk_size >= 1
    accumulator = []
    for x in input_stream:
        accumulator.append(x)
        if len(accumulator) == chunk_size:
            yield accumulator
            accumulator = []
    if accumulator:
        yield accumulator

编辑

受kreativitea的回答启发，这是使用 islice 的解决方案，这很简单&不需要后期过滤，

Edit

Inspired by kreativitea's answer, here's a solution with islice, which is straightforward & doesn't require post-filtering,

from itertools import islice

def chunk_input_stream(input_stream, chunk_size):
    while True:
        chunk = list(islice(input_stream, chunk_size))
        if chunk:
            yield chunk
        else:
            return

# test it with list(chunk_input_stream(iter([1, 2, 3, 4]), 3))

推荐答案

[感谢OP的更新版本：我一直在将 yield from 扔给自从我升级之后，它的视线就消失了，我什至没有想到我在这里不需要它。]

[Updated version thanks to the OP: I've been throwing yield from at everything in sight since I upgraded and it didn't even occur to me that I didn't need it here.]

哦，这到底是什么：

from itertools import takewhile, islice, count

def chunk(stream, size):
    return takewhile(bool, (list(islice(stream, size)) for _ in count()))

：

>>> list(chunk((i for i in range(3)), 3))
[[0, 1, 2]]
>>> list(chunk((i for i in range(6)), 3))
[[0, 1, 2], [3, 4, 5]]
>>> list(chunk((i for i in range(8)), 3))
[[0, 1, 2], [3, 4, 5], [6, 7]]

警告：以上内容与OP的 chunk_input_stream 存在相同的问题输入是一个列表。您可以通过额外的 iter（）包装来解决此问题，但这并不那么漂亮。从概念上讲，使用 repeat 或 cycle 可能比 count（），但由于某种原因我正在计算字符数。 ：^）

Warning: the above suffers the same problem as the OP's chunk_input_stream if the input is a list. You could get around this with an extra iter() wrap but that's less pretty. Conceptually, using repeat or cycle might make more sense than count() but I was character-counting for some reason. :^)

[FTR：不，我仍然对此并不完全认真，但是，嘿，这是星期一。]

[FTR: no, I'm still not entirely serious about this, but hey-- it's a Monday.]

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