python程序设计基础（六）
今天讲述列表（list）推导式。
上次简单解释列表推导式的定义以及实例，下面深入了解推导式。其语法格式为 [表达式 for 迭代变量 in可迭代对象 [if 条件表达式]]，其中可迭代对象指存储了元素的一个容器对象，且容器中的元素可以通过__iter__( )方法或__getitem__( )方法访问。包括列表、元组、字典、字符串。
下面通过例子说明。
01
一次循环
一次循环，x依次在range（10）这一范围内取值，并满足条件x > 5。
02
两次循环
两次循环,可以理解为x变量在某一确定值的情况下，y变量在范围内遍历取值，x为外层循环，y为内层循环。
03
三次循环
三次循环道理一致。x,y,z三个变量，层次依次递增。可以理解为在开始时，x，y确定的情况下z取值，y变化，z取值；x变化，y取值，z取值，层层递进。
04
拓展
针对需求不一致，灵活使用列表推导式。比如，实现5次列举x在0到3之间并以列表的形式出现。
最后，列表推导式有执行顺序，从左往右，语句的层次越高。
英文翻译
Today we will talk about list comprehensions.
Last time we briefly explained the definition and examples of list comprehensions, and let’s learn more about comprehensions.
Its grammatical format is [expression for iterative variable in iterable object [if conditional expression]], where the iterable object refers to a container object that stores the elements, and the elements in the container can be through the __iter__() method or __getitem__ () Method access. Including lists, tuples, dictionaries, and strings.
The following is an example to illustrate.
1. In one cycle, x takes values ?in the range (10) in turn, and satisfies the condition x> 5.
2. Two loops can be understood as when the x variable is at a certain value, the y variable traverses the value within the range, x is the outer loop, and y is the inner loop.
The three cycles are the same. The three variables x, y, and z increase in order. It can be understood that at the beginning, when x and y are determined, z takes the value, y changes, and z takes the value; x changes, y takes the value, and z takes the value, progressively.
3. For inconsistent requirements, use list comprehensions flexibly. For example, implement 5 times to enumerate x between 0 and 3 and qualify as a list.
Finally, the list comprehension has the order of execution, from left to right, the higher the level of the statement。
参考资料：菜鸟教程
翻译：Google翻译
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