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Python学习day03 - Python基础（1）

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1. 执行Python程序的两种方式

(1)交互式（Jupyter）

优点:运行一句执行一句

缺点:关闭即消失#

(2)命令行式（pycharm）

优点:可以一直保存

缺点:全部写完才能调试bug虽然txt文件可以运行,但尽量用py文件

2. 变量

(1)定义变量

•             变化的世间万物的状态

(2)变量的组成

•             变量名（接收变量值） = （赋值符号）变量值（数值） -> 定义变量

(3)变量的命名规范

1.          变量名必须由数字/字母/下划线/组成
height of nick = 180 #下划线只在连接时候用#

2.
变量名具有可读性（实际意义）存不是目的，取才是目的

3.
不要使用关键字（具有某种特殊意义的字符）

(4)变量名的两种风格

height_of_nick =180# 下换线式#
heightOfNick
=180   # 驼峰体

3. 常量

•
不变的量,常量本质上还是个变量，只不过变量名全大写约定俗成为了常量，一般不改变常量。

•
约定俗成，全部大写去定义的变量即为常量

4. Python变量内存管理

(1) Python垃圾回收机制

•
简单来说，Python会自动把引用计数为零的变量处理掉，释放其内存，不像其他语言需要手动把之前定义变量占用的内存释放掉。

(2) 小整数池

•
Python实现int的时候有个小整数池。为了避免因创建相同的值而重复申请内存空间所带来的效率问题， Python解释器会在启动时创建出小整数池，范围是[-5,256]，该范围内的小整数对象是全局解释器范围内被重复使用，永远不会被垃圾回收机制回收。

•
需要注意的是，上述理论如果需要验证，需要在终端cmd中或者Jupyter中才可以，pycharm中验证不了小整数池的存在哦~因为pycharm处于对性能的考虑，会扩大小整数池的范围，范围很大，非常大。

5. 花式赋值

(1) 链式赋值

a = 10

b = 10

c = 10

a=b=c=10

print(a,b,c)

(2)交叉赋值

x =10
y =20
print('y:',id(y))
print('x:',id(x))
x,y = y,x
print('y:',id(y))
print('x:',id(x))

交叉赋值还可以用于解压缩，在后文中会进行说明。

6. 注释

(1)单行注释和多行注释

单行注释只要在行首加#即可，快捷键ctrl + /

多行注释则是在需要注释部分的上下分别加```

# b = 5
```
a =12
print(a)
```

(2)添加注释的常见位置

•
代码块的上方，负责解释该段代码块的意义

•
一行代码的后方，负责解释该行代码的意义

7. tip：

pycharm的几个使用便捷选项~

（1）如何tab补齐不区分大小写。

File --> Settings --> Editor
--> General --> Code Comlpletion

在右侧，Case sensitive completion:后面的选项改成None，即可实现使用tab补齐时不区分大小写都可以补齐

（2）如何自动添加文件头部内容

File --> Settings --> Editor
--> File and Code Templates

右侧，有Python Script选项，点中后，右侧空白框里即可输入想要添加的文件头部的内容，亲测有效。

（3）推荐学习python的几个网址~

•
菜鸟教程

•
廖雪峰的官方网站

•
博客园咸鱼Chen的 Python从入门到放弃。

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