python基础（变量、基础数据类型、流程控制）

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今日内容

变量

• 定义：将程序运行中的中间值临时存储起来，以便再次使用

• 变量一般用于后期开发使用

• 变量名使用规范：

  1. 数字、字母、下划线组成

  2. 不能以数字开头

  3. 禁止使用python关键字

     ['False', 'None', 'True', 'and', 'as', 'assert', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']

  4. 变量名要具有可描述性

  5. 变量名要区分大小写

  6. 变量名不能使用拼音和中文

  7. 推荐写法

     7.1驼峰体

     Alexdfkasd = "adsdf"

     7.2下划线

     alex_name = "asdfasdf"

常量及注释

常量

• 定义：变量名大写就是常量

• 注意：其他语言中常量不能被修改，python中的常量可以被修改，但是一般不要修改

• 常量一般用于文件配置

注释

• 定义：给一些晦涩难懂的代码进行注释

• 单行注释：# 注释后的代码不会被执行，且不占内存

• 多行注释：''' '''或”“” “”“可以换行

• PEP8开发规范：代码不宜过长，超过界面分界线

基础数据类型

int整型

• 用于计算和比较：+、-、*、/、

str字符串

“ ”

‘ ’

“‘ ”’

bool布尔值

True False

str(int)时字符串内容只能是数字

python2和python3的区别

• python2

  • 源码不统一
  • 代码有重复
  • print不用加括号
  • 做除法时，输出为整数
  • raw_input获取到全为字符串，input获取到什么类型，输出就是什么类型

• python3

  • 代码统一
  • 代码没有重复
  • print要加括号
  • 做除法时，输出是浮点型
  • input获取到的全为字符串

流程控制语句

• if嵌套

  • 如果 条件：

    缩进 结果

    缩进 如果 条件：

    缩进 结果

    用于判断

• if else 二选一

  • 如果 条件：

  • 缩进 结果

    否则：

    缩进 结果

• if elif elif elif 多选一或零

  • 如果 条件：

    缩进 结果

    在如果 条件：

    缩进 结果

    在如果 条件：

    缩进 结果