Add clarification to zip's documentation

Documentation

Using zip on iterators of variable length results in a behavior that I believe would benefit from some additional clarification in the documentation. Take the following example:

>>> a = list(range(3))
>>> b = iter(range(100))
>>> list(zip(a, b))
[(0, 0), (1, 1), (2, 2)]
>>> list(zip(a, b))
[(0, 3), (1, 4), (2, 5)]

This is expected behavior as zip simply stops at the end of the shortest iterable, in this case a. When calling zip again a is restarted whilst b carries on from 3.

The unexpected behavior comes about when we swap the arguments putting the longer iterator as the first argument.

>>> a = list(range(3))
>>> b = iter(range(100))
>>> list(zip(b, a))
[(0, 0), (1, 1), (2, 2)]
>>> list(zip(b, a))
[(4, 0), (5, 1), (6, 2)]

Rather than carrying on from 3 like in the previous example we get a 4. I understand this is due to b being consumed during the zip and there is no way to know which iterator will yield a StopIteration first and so this is the intended behavior.

It may be beneficial to highlight this edge case in the documentation and make the recommendation to try and put the shortest iterator first.

從 Python 內建函式 zip 的文件開始，檢視其中如何描述在最短的 iterable 處停止。明確說明 iterator 可能會在達到 StopIteration 之前就被消耗，並記錄所示的引數順序邊界情況，包括建議將最短的 iterator 放在最前面。完成的標準是 zip 文件中清楚說明了該行為和建議。