March 2022
Intermediate to advanced
522 pages
13h 52m
Chinese
Content preview from Python语言及其应用（第2版）
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74
｜
第
6
章
6.2.4
使用
range()
生成数字序列
range()
函数可以返回指定范围内的一系列数字，无须事先创建和存储大型数据结构（比
如列表或元组）。这样就可以创建大区间值，而不至于耗尽所有内存，导致程序崩溃。
range()
的用法类似于分片：
range(
start
,
stop
,
step
)
。如果忽略
start
，那么范围会从
0
开始。唯一需要的值是
stop
。和切片一样，最后创建的值位于
stop
之前。
step
的默认值
为
1
，但也可以使用
-1
生成数字序列。
和
zip()
一样，
range()
返回的是一个
可迭代
的对象，所以需要用
for ... in
来遍历每个
值，或者将对象转换为一个序列（如列表）。下面来生成序列
0, 1, 2
：
>>> for x in range(0,3):
... print(x)
...
0
1
2
>>> list( range(0, 3) )
[0, 1, 2]
下面创建从
2
到
0
的序列：
>>> for x in range(2, -1, -1):
... print(x)
...
2
1
0
>>> list( range(2, -1, -1) )
[2, 1, 0]
下面的代码片段使用步进值
2
获得
0
和
10
之间的偶数。
>>> list( range(0, 11, 2) )
[0, 2, 4, 6, 8, 10]
6.3
其他迭代器
第
14
章展示了迭代文件。第
10
章介绍了如何迭代自定义对象。此外，第
11
章还讨论了
itertools
，这是一个标准的
Python
模块，包含了许多实用的便捷写法。 ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.