Common operators 9.21

One ,python The variable of

：
（1） meaning ：1, The amount that can change while the program is running ;
2, Memory variable with name
（2） How to define variables ：
Variable name = A variable's value
Strong data type language ：Java c c++ c#
data type Variable name = A variable's value
?int num 100
Weak data type Language ：python PHP ruby
（3） Named rules ：
1, Variable names must have numbers , Case letters , Underline
2, Variable name cannot start with a number
3, You cannot use keywords or reserved words as variable names
4, Name variables as meaningful as possible
5, Try to follow the underline （name_age） Or camel Peak method （ Initial lowercase , Other words are capitalized ）

Two , Common operators

 Arithmetic operator ：+  - * /     %  //   **
 Logical operators ：and .or .not
 Relational operator :   >  < .>=.<=.==.!
 Assignment operator ：
          =
         +=
          -=
          /=
         //=
          **=

Self addition and self subtraction operators , Be careful ：python There is no such operator .