問題描述
我在互聯網上找不到任何有效的例子，我可以看到它們之間的區別以及為什么要選擇一個而不是另一個.
I could not find any valid example on the internet where I can see the difference between them and why to choose one over the other.
推薦答案
第一個接受 0 個或多個參數，每個參數是一個可迭代對象，第二個接受一個預期生成可迭代對象的參數:
The first takes 0 or more arguments, each an iterable, the second one takes one argument which is expected to produce the iterables:
from itertools import chain
chain(list1, list2, list3)
iterables = [list1, list2, list3]
chain.from_iterable(iterables)
但 iterables 可以是任何產生可迭代對象的迭代器:
but iterables can be any iterator that yields the iterables:
def gen_iterables():
for i in range(10):
yield range(i)
itertools.chain.from_iterable(gen_iterables())
使用第二種形式通常是一種方便的情況，但由于它會延遲循環輸入可迭代對象，因此它也是鏈接無限個有限迭代器的唯一方法:
Using the second form is usually a case of convenience, but because it loops over the input iterables lazily, it is also the only way you can chain an infinite number of finite iterators:
def gen_iterables():
while True:
for i in range(5, 10):
yield range(i)
chain.from_iterable(gen_iterables())
上面的例子將給你一個迭代，它產生一個循環的數字模式，它永遠不會停止，但永遠不會消耗比單個 range() 調用所需更多的內存.
The above example will give you a iterable that yields a cyclic pattern of numbers that will never stop, but will never consume more memory than what a single range() call requires.
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