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

我喜欢这种方法。它感觉简单而不神奇,支持所有可迭代类型,并且不需要导入。

def chunk_iter(iterable, chunk_size):
it = iter(iterable)
while True:
    chunk = tuple(next(it) for _ in range(chunk_size))
    if not chunk:
        break
    yield chunk

其他回答

NumPy很简单:

ints = array([1, 2, 3, 4, 5, 6, 7, 8])
for int1, int2 in ints.reshape(-1, 2):
    print(int1, int2)

输出:

1 2
3 4
5 6
7 8

修改自Python的itertools文档中的Recipes部分:

from itertools import zip_longest

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

例子

grouper('ABCDEFG', 3, 'x')  # --> 'ABC' 'DEF' 'Gxx'

注意:在Python 2上使用izip_longest而不是zip_longest。

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

还有另一个答案,它的优点是:

1)容易理解 2)适用于任何可迭代对象,而不仅仅是序列(上面的一些答案会阻塞文件句柄) 3)不立即将数据块加载到内存 4)不会在内存中生成对同一迭代器的块长的引用列表 5)在列表的末尾没有填充填充值

话虽如此,我还没有计算它的时间,所以它可能比一些更聪明的方法慢,而且考虑到用例,一些优势可能是无关紧要的。

def chunkiter(iterable, size):
  def inneriter(first, iterator, size):
    yield first
    for _ in xrange(size - 1): 
      yield iterator.next()
  it = iter(iterable)
  while True:
    yield inneriter(it.next(), it, size)

In [2]: i = chunkiter('abcdefgh', 3)
In [3]: for ii in i:                                                
          for c in ii:
            print c,
          print ''
        ...:     
        a b c 
        d e f 
        g h 

Update: A couple of drawbacks due to the fact the inner and outer loops are pulling values from the same iterator: 1) continue doesn't work as expected in the outer loop - it just continues on to the next item rather than skipping a chunk. However, this doesn't seem like a problem as there's nothing to test in the outer loop. 2) break doesn't work as expected in the inner loop - control will wind up in the inner loop again with the next item in the iterator. To skip whole chunks, either wrap the inner iterator (ii above) in a tuple, e.g. for c in tuple(ii), or set a flag and exhaust the iterator.

下面是一个支持生成器的无导入chunker:

def chunks(seq, size):
    it = iter(seq)
    while True:
        ret = tuple(next(it) for _ in range(size))
        if len(ret) == size:
            yield ret
        else:
            raise StopIteration()

使用示例:

>>> def foo():
...     i = 0
...     while True:
...         i += 1
...         yield i
...
>>> c = chunks(foo(), 3)
>>> c.next()
(1, 2, 3)
>>> c.next()
(4, 5, 6)
>>> list(chunks('abcdefg', 2))
[('a', 'b'), ('c', 'd'), ('e', 'f')]