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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数据：类型、值、变量和名称
｜
23
下面这些都是有效名称。
• a
• a1
• a_b_c___95
• _abc
• _1a
下面这些都是无效名称。
• 1
• 1a
• 1_
• name!
• another-name
2.6
赋值
在
Python
中，可以使用
=
为变量赋值。
我们在小学算术中都学过，
=
表示
等于
。那么为什么包括
Python
在内的许多
计算机语言使用
=
进行赋值呢？原因之一是，标准键盘缺乏逻辑上的替代方
案，比如左箭头键，而
=
似乎也没那么让人困惑。另外，在计算机程序中，
赋值操作远比等量测试用得多。
程序不同于代数，你在学校学习数学的时候，看到的方程是这样的：
y = x + 12
可以通过为
x
代入值来解这个方程。如果将
5
代入
x
，
5 + 12
等于
17
，所以
y
的值是
17
。
将
6
代入
x
的话，
y
的值则为
18
，以此类推。
计算机程序语句看起来像方程，但含义完全不同。在
Python
和其他计算机语言中
，
x
和
y
是
变量
。
Python
知道像
12
或
5
这样的纯数位序列是整数。下面这个小
Python
程序模拟了
方程，打印出
y
的结果：
>>> x = 5
>>> y = x + 12
>>> y
17
这是数学和程序之间的一个很大的不同。在数学中，
=
代表两侧的
等量关系
；在程序中，
=
则表示
赋值
：将右侧的值赋给左侧的变量。
另外，在程序中，右侧的一切都需要有值（这称为
初始化
）。右侧既可以是字面值，也可
以是已经赋过值的变量，或是二者的组合。
Python
知道
5
和
12
都是字面整数。第一行将
整数值
5
赋给变量
x
。现在可以在下一行中使用变量 ...
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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.