我有一个Python脚本,它把一个整数列表作为输入,我需要一次处理四个整数。不幸的是,我无法控制输入,否则我将它作为一个四元素元组列表传入。目前,我以这种方式迭代它:

for i in range(0, len(ints), 4):
    # dummy op for example code
    foo += ints[i] * ints[i + 1] + ints[i + 2] * ints[i + 3]

不过,它看起来很像“C-think”,这让我怀疑有一种更python的方式来处理这种情况。该列表在迭代后被丢弃,因此不需要保留。也许这样会更好?

while ints:
    foo += ints[0] * ints[1] + ints[2] * ints[3]
    ints[0:4] = []

不过,感觉还是不太对。: - /

相关问题:在Python中如何将列表分割成大小均匀的块?


当前回答

import itertools
def chunks(iterable,size):
    it = iter(iterable)
    chunk = tuple(itertools.islice(it,size))
    while chunk:
        yield chunk
        chunk = tuple(itertools.islice(it,size))

# though this will throw ValueError if the length of ints
# isn't a multiple of four:
for x1,x2,x3,x4 in chunks(ints,4):
    foo += x1 + x2 + x3 + x4

for chunk in chunks(ints,4):
    foo += sum(chunk)

另一种方法:

import itertools
def chunks2(iterable,size,filler=None):
    it = itertools.chain(iterable,itertools.repeat(filler,size-1))
    chunk = tuple(itertools.islice(it,size))
    while len(chunk) == size:
        yield chunk
        chunk = tuple(itertools.islice(it,size))

# x2, x3 and x4 could get the value 0 if the length is not
# a multiple of 4.
for x1,x2,x3,x4 in chunks2(ints,4,0):
    foo += x1 + x2 + x3 + x4

其他回答

如果列表很大,执行效率最高的方法是使用生成器:

def get_chunk(iterable, chunk_size):
    result = []
    for item in iterable:
        result.append(item)
        if len(result) == chunk_size:
            yield tuple(result)
            result = []
    if len(result) > 0:
        yield tuple(result)

for x in get_chunk([1,2,3,4,5,6,7,8,9,10], 3):
    print x

(1, 2, 3)
(4, 5, 6)
(7, 8, 9)
(10,)

因为没有人提到它,这里有一个zip()解决方案:

>>> def chunker(iterable, chunksize):
...     return zip(*[iter(iterable)]*chunksize)

只有当你的序列长度总是能被块大小整除时,它才有效,或者如果后面的块不能整除,你就不关心它。

例子:

>>> s = '1234567890'
>>> chunker(s, 3)
[('1', '2', '3'), ('4', '5', '6'), ('7', '8', '9')]
>>> chunker(s, 4)
[('1', '2', '3', '4'), ('5', '6', '7', '8')]
>>> chunker(s, 5)
[('1', '2', '3', '4', '5'), ('6', '7', '8', '9', '0')]

或者使用itertools。返回一个迭代器而不是一个列表:

>>> from itertools import izip
>>> def chunker(iterable, chunksize):
...     return izip(*[iter(iterable)]*chunksize)

填充可以固定使用@ΤΖΩΤΖΙΟΥ的答案:

>>> from itertools import chain, izip, repeat
>>> def chunker(iterable, chunksize, fillvalue=None):
...     it   = chain(iterable, repeat(fillvalue, chunksize-1))
...     args = [it] * chunksize
...     return izip(*args)

一行程序,特别的解决方案,以4 -大小的块迭代列表x

for a, b, c, d in zip(x[0::4], x[1::4], x[2::4], x[3::4]):
    ... do something with a, b, c and d ...

在我的特殊情况下,我需要填充项目,以重复最后一个元素,直到它达到大小,所以我改变了这个答案,以适应我的需要。

大小为4的输入输出示例:

Input = [1,2,3,4,5,6,7,8]
Output= [[1,2,3,4], [5,6,7,8]]

Input = [[1,2,3,4,5,6,7]]
Output= [[1,2,3,4], [5,6,7,7]]

Input = [1,2,3,4,5]
Output= [[1,2,3,4], [5,5,5,5]]
def chunker(seq, size):
    res = []
    for el in seq:
        res.append(el)
        if len(res) == size:
            yield res
            res = []
    if res:
        res = res + (size - len(res)) * [res[-1]] 
        yield res

使用小的函数和东西真的不吸引我;我更喜欢使用切片:

data = [...]
chunk_size = 10000 # or whatever
chunks = [data[i:i+chunk_size] for i in xrange(0,len(data),chunk_size)]
for chunk in chunks:
    ...