Python内置函数(67)——zip

英文文档：

zip(*iterables)

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

Returns an iterator of tuples, where the i-th tuple contains the i-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.

The left-to-right evaluation order of the iterables is guaranteed. This makes possible an idiom for clustering a data series into n-length groups using zip(*[iter(s)]*n). This repeats the same iterator n times so that each output tuple has the result of n calls to the iterator. This has the effect of dividing the input into n-length chunks.

说明：

　　1. 函数功能是聚合传入的每个迭代器中相同位置的元素，返回一个新的元组类型迭代器。

>>> x = [1,2,3]
>>> y = [4,5,6]
>>> xy = zip(x,y)
>>> xy #xy的类型是zip类型
<zip object at 0x0429C828>
#导入Iterable
>>> from collections import Iterable
>>> isinstance(xy,Iterable) #判断是否可迭代对象
True
>>> list(xy) #结果
[(1, 4), (2, 5), (3, 6)]

　　2. 如果传入的迭代器长度不一致，最短长度的迭代器迭代结束后停止聚合。

>>> x = [1,2,3] #长度3
>>> y = [4,5,6,7,8] #长度5
>>> list(zip(x,y)) # 取最小长度3
[(1, 4), (2, 5), (3, 6)]

　　3. 如果只传入一个迭代器，则返回的单个元素元组的迭代器。

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

　　4. 如果不传入参数，则返回空的迭代器。

>>> list(zip())
[]

　　5. zip(*[iter(s)]*n)等效于调用zip(iter(s),iter(s),...,iter(s))。

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

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

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