python - 根据上一个和下一个元素将元素插入到列表中

Question

我正在尝试将一个新元组添加到元组列表(按元组中的第一个元素排序)，其中新元组包含列表中前一个元素和下一个元素的元素。

例子:

oldList = [(3, 10), (4, 7), (5,5)]
newList = [(3, 10), (4, 10), (4, 7), (5, 7), (5, 5)]

(4,10) 是在 (3,10) 和 (4,7) 之间构建和添加的。

Construct (x,y) from (a,y) and (x,b)

我试过使用 enumerate() 在特定位置插入，但这并不能真正让我访问下一个元素。

Answer 1

oldList = [(3, 10), (4, 7), (5,5)]

def pair(lst):
    # create two iterators
    it1, it2 = iter(lst), iter(lst)
    # move second to the second tuple
    next(it2)
    for ele in it1:
        # yield original
        yield ele
        # yield first ele from next and first from current
        yield (next(it2)[0], ele[1])

这会给你:

In [3]: oldList = [(3, 10), (4, 7), (5, 5)]

In [4]: list(pair(oldList))
Out[4]: [(3, 10), (4, 10), (4, 7), (5, 7), (5, 5)]

显然我们需要做一些错误处理来处理不同的可能情况。

如果愿意，您也可以使用单个迭代器来完成此操作:

def pair(lst):
    it = iter(lst)
    prev = next(it)
    for ele in it:
        yield prev
        yield (prev[0], ele[1])
        prev = ele
    yield (prev[0], ele[1])

您可以使用 itertools.tee代替调用 iter:

from itertools import tee
def pair(lst):
    # create two iterators
    it1, it2 = tee(lst)
    # move second to the second tuple
    next(it2)
    for ele in it1:
        # yield original
        yield ele
        # yield first ele from next and first from current
        yield (next(it2)[0], ele[1])