每隔一个元素向列表中添加一个元素

Question

我想每隔一个元素向现有列表中插入一个元素。

假设列表是fruits = ["banana", "apple", "mango", "kiwi"]，要添加元素"peach"，我要做的是：

fruits = ["banana", "apple", "mango", "kiwi"]
fruits_2 = list(fruits)

for i in range(len(fruits)):
    fruits_2.insert(2*i + 1, "peach")

print(fruits_2)

输出是

['banana', 'peach', 'apple', 'peach', 'mango', 'peach', 'kiwi', 'peach']

这就是我想要的，但是我感觉可能有一种更好且更简洁的方法，而无需创建第二个列表。

Answer 1

用zip，连同itertools.repeat和itertools.chain。

>>> from itertools import chain, repeat
>>> fruits = ["banana", "apple", "mango", "kiwi"]
>>> list(chain.from_iterable(zip(fruits, repeat("peach"))))
['banana', 'peach', 'apple', 'peach', 'mango', 'peach', 'kiwi', 'peach']

repeat创建的无限序列'peach'。zip创建一系列对，由水果中的一个项目和一个实例组成'peach'。chain.from_iterable将对的序列“平化”为单个序列，并list从该序列中生成具体列表。

看中间步骤：

>>> from itertools import islice
>>> list(islice(repeat("peaches"), 5))
['peaches', 'peaches', 'peaches', 'peaches', 'peaches']

>>> zip(fruits, repeat("peaches"))
[('banana', 'peaches'), ('apple', 'peaches'), ('mango', 'peaches'), ('kiwi', 'peaches')]

这种方法可以归结为一系列appends新清单，例如

result = []
for x in fruits:
    result.append(x)
    result.append("peaches")

但是append，您无需对参数进行硬编码，而是从一对迭代器中获取它们：

def peach_source():
    while True:
        yield "peach"

def fruit_source(fruits):
    for x in fruits:
        yield x

result = []
peaches = peach_source()
fruits = fruit_source(fruits)  # Yes, this is highly redundant; just showing the similarity to peach_source
done = False
while not done:
    try:
        result.append(next(fruits))
    except StopIteration:
        done = True
    result.append(next(peaches))

itertools.repeatpeach_source为您创造。zip处理获取水果和获取桃子之间的交替。chain.from_iterable定义附加到的操作result，并list实际执行附加操作。