序列

原文第2章第3节

分解序列(sequence unpacking)

The pattern of binding multiple names to multiple values in a fixed-length sequence。
序列中各值赋予不同变量名。

>>> pairs = [[1, 2], [2, 2], [2, 3], [4, 4]]

>>> same_count = 0

如果执行下列代码：

>>> for x, y in pairs:
        if x == y:
            same_count = same_count + 1

就可以得到：

>>> same_count
2

列表推导式(list comprehension)

An expression that can performs such a sequence processing operation which can be expressed by evaluating a fixed expression for each element in a sequence and collecting the resulting values in a result sequence.
一行代码直接完成对列表的便利操作并返回值。
例如，

>>> odds = [1, 3, 5, 7, 9]
>>> [x+1 for x in odds]
[2, 4, 6, 8, 10]

# Another Example
>>> [x for x in odds if 25 % x == 0]
[1, 5]

通式：

[<map expression> for <name> in <sequence expression> if <filter expression>]

列表推导式的效果也可以用高阶函数的方式来达到，但前者更为常见（个人觉得前者更利于理解）。

数据类型的闭合性

In general, a method for combining data values has a closure property if the result of combination can itself be combined using the same method.
例如，列表自身可以组成列表的元素。