08-Variables and reserved words

08-Variables and reserved words

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1: reserved words

使用以下代码查看Python中的保留字

Demo:

import keyword
print(keyword.kwlist)

Output:

['False', 'None', 'True', 'and', 'as', 'assert', 'async', 'await', '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']

These reserved words generally cannot be used as identifiers

2: Identifier

1. What is an identifier?

   Variables, functions, classes, modules, and other objects are namedidentifier

2. Identifier naming rules

   • Can only be named with letters, numbers, and underscores
   • Cannot start with a number
   • Cannot be a reserved word
   • Strictly case sensitive

Three: Variables

1. what is a variable

   A variable is a labeled box in memory.

2. Definition and use of variables

   • Variables consist of three parts

     1. Identification: represents the memory address where the object is stored, using id( obj )Obtain
     2. Type: The data type of the object, use type( obj )Obtain
     3. Value: The specific data stored in the object, use print( obj )print out directly

   • name = "Gui Gui"

     Analysis:

     ​ *name: * identifier, which is the variable name

     ​ *=: *assignment operator

     ​ *Guigui:*give the value of the variable

3. Multiple assignment of variables

   • Variables can be assigned multiple times, and new values ​​will overwrite old ones.

Demo:

# 变量
name = "桂桂";
print("内存地址：",id(name))
print("类型：",type(name))
print("值：",name)

# 多次赋值
age = 1234;
print("id：",id(age)," type：",type(age)," 值：",age)
age = 5678;
print("id：",id(age)," type：",type(age)," 值：",age)

Output:

内存地址： 2537550061808
类型： <class 'str'>
值： 桂桂

id： 2537544939152  type： <class 'int'>  值： 1234
id： 2537551076816  type： <class 'int'>  值： 5678