python zip

zip接受多个序列对象作为参数，返回一个tuple的序列，细节如下：

zip(*iterables)

Make an iterator that aggregates elements from each of the iterables.

Returns an iterator of tuples, where the i-th tuple contains thei-th element from each of the argument sequences or iterables. The iterator stops when the shortest input iterable is exhausted. With a single iterable argument, it returns an iterator of 1-tuples. With no arguments, it returns an empty iterator.

>>> x = [1, 2, 3]
>>> y = [4, 5, 6]
>>> zipped = zip(x, y)
>>> list(zipped) #python3以后，需要list
[(1, 4), (2, 5), (3, 6)]
>>> x2, y2 = zip(*zip(x, y))#解压
>>> x == list(x2) and y == list(y2)
True

1）只有一个序列作为参数时：

>>> x = [1,2,3]

>>> x1 = zip(x)
>>> list(x1)
[(1,), (2,), (3,)]

2）无参时

>>> list(zip())
[]

3）zip([x]*3) 与 zip(*[x]*3)

>>> x = [1,2,3]

>>> [x]*3
[[1, 2, 3], [1, 2, 3], [1, 2, 3]]

>>> list(zip([x]*3))
[([1, 2, 3],), ([1, 2, 3],), ([1, 2, 3],)]
>>> list(zip(*[x]*3))
[(1, 1, 1), (2, 2, 2), (3, 3, 3)]

原因：在函数调用中使用*list/tuple的方式表示将list/tuple分开，作为位置参数传递给对应函数（前提是对应函数支持不定个数的位置参数）