python zip()

zip函数接受任意多个（包括0个和1个）序列作为参数，返回一个tuple列表。

ex1

x = [1, 2, 3]
y = [4, 5, 6]
z = [7, 8, 9]
xyz = zip(x, y, z)
print xyz

[(1, 4, 7), (2, 5, 8), (3, 6, 9)]

ex2

x = [1, 2, 3]
y = [4, 5, 6, 7]
xy = zip(x, y)
print xy

[(1, 4), (2, 5), (3, 6)]

ex3

x = [1, 2, 3]
x = zip(x)
print x

[(1,), (2,), (3,)]

ex4

x = zip()
print x

[]

ex5

x = [1, 2, 3]
y = [4, 5, 6]
z = [7, 8, 9]
xyz = zip(x, y, z)
u = zip(*xyz)
print u

[(1, 2, 3), (4, 5, 6), (7, 8, 9)]

一般认为这是一个unzip的过程，它的运行机制是这样的：

在运行zip(*xyz)之前，xyz的值是：[(1, 4, 7), (2, 5, 8), (3, 6, 9)]

那么，zip(*xyz) 等价于 zip([(1, 4, 7), (2, 5, 8), (3, 6, 9)])

所以，运行结果是：[(1, 2, 3), (4, 5, 6), (7, 8, 9)]

ex6

x = [1, 2, 3]
r = zip(*[x]*3)
print r

[(1, 1, 1), (2, 2, 2), (3, 3, 3)]

它的运行机制是这样的：

[x]生成一个列表的列表，它只有一个元素x

[x] * 3生成一个列表的列表，它有3个元素，[x, x, x]

zip(* [x] * 3)的意思就明确了，zip(x, x, x)