How to use python variable data types and operators

An ordinary three single quotes

An ordinary character\

##An ordinary triple double quotation mark

##\t

• String encoding: The computer can only recognize binary, so how to store the string in the computer

The computer cannot store it directly String, but we can encode the characters, for example, use 65 to represent uppercase character A, 66 to represent uppercase character B... etc. This representation method is the American ASCII code, which can only represent 127 characters, but for Americans That's enough. Once we can use integers to represent characters, we can easily represent integers in binary, and strings can be easily stored in the computer.
But there are many languages ​​in other countries that cannot be represented by ASCII. All ISO organizations have introduced unicode codes, which are used to represent characters in any language. Unicode codes are also called universal codes and universal codes. Represents any character in any language. There are many representation methods of unicdoe code, such as: utf-8, utf-16, utf-32, etc. The most commonly used one is utf-8. utf-8 is a variable-length encoding, which means that a character may use one byte or three bytes.
Commonly used Chinese encodings generally use GBK encoding, using 2 Bytes represent a Chinese character

1.2 Type judgment

We can use type and isinstance to test and judge the data type

#type用法：
type(obj)
功能：返回obj的数据类型
参数：obj是你要测试变量或数值
示例：
age = 10
name = 'hello'
print(type(name),type(age))
#判断变量是否是指定类型
if type(age) is int:
print('是')
else:
print('否')

#isinstance用法：
isinstance(obj,typename)
功能：判断obj是否是指定类型，是返回True,否返回False
参数： objobj是你要判断的变量或数值
typename是指定数据类型,可以是int,float,str等。也可是一个
类型的元组,例如:(int,float)
示例：
age = 10
name = 'hello'
print(isinstance(age,int))
print(isinstance(name,(str,int)) #只要name是str或int的一种就返回True

if isinstance(age,int):
print('是')
else:
print('否')

#type和isinstance的区别
type判断基本类型是没问题的，但无法判断子类对象是父类的一种
isinstance可以判断子类对象是父类的一种
class A:
pass
class B(A):
pass

objA = A()
objB = B()

#输出否
if type(objB) is A:
print('是')
else:
print('否')
print(isinstance(objB,A)) #True

Conclusion:Use first isinstance

2. Operators and expressions

In order to calculate the results in mathematics, we will write some formulas to calculate, for example:

30 5

This is a calculation formula in mathematics. There are similar formulas in python for calculation, called expressions. In the expression, 30 and 5 are called operands, called operators. The purpose of an expression is to compute a result. Expression composition:

• The most basic expressions are some numerical values, variables, and functions, for example: 3, a (variable) print(‘hello’)

• Complex expressions are composed of basic expressions plus appropriate operators: 3 a

Based on the above, the so-called expression is composed of operands and operators An expression that conforms to python syntax. To write expressions, you first need to learn operators. There are two things to know about operators

• Calculation order: Is it calculated from left to right or right to left

• Priority: For example, multiplication and division first, then addition and subtraction

2.1 Arithmetic operators

a = 20
b = 10

• Calculation formula of modular operation: r = a % b = a - n * b, where n is the largest integer less than a/b

• Integer division (//) operation if there is an operation The number is a floating point number, and the result is a floating point number

• Uses: Determining parity, determining whether it is divisible, greatest common divisor, narcissus number

• 2.3 Mathematical functions

2.4 随机函数

获取随机数，需要引入random库。

import random

注意：

• 优先级： ** >正负号 > // % * / > + -

• 从左向右算

• 在幂运算和一元运算符联合计算时，从右向左算，例如： -1 ** 2 = -1

2.5 赋值运算符

a = 5; b = 10; c = 20

注意：

• 赋值运算符左边必须是变量

• 从右向左算

• 没有赋值表达式

• 所有赋值运算符优先级相同，赋值运算符优先级非常低，仅高于成员运算符和身份运算符、逻辑运算符

• 注意在复合赋值中

a = 2
b = 3
a *= b + 2 #等价于 a = a * (b + 2)
print(a) # a = 10

2.6 关系运算

关系运算就是比较运算，如果表达式成立，返回True，否则返回False。关系运算的结果是布尔值。