A, Python 3 entry of the string, the operator

3, the operator

1. Assignment operator and the extended assignment operator

   a_1 = 123
   print(a_1)
   
   a_2 = 20
   a_2 -= 5        
   print(a_2)
   

   123

   15

2. Arithmetic Operators

   div_1 = 5/3
   print(div_1)
   
   div_2 = 5//3     # 整除
   print(div_2)
   
   div_3 = 5.3//3.2
   print(div_3)
   
   mod = 23%7       # 求余
   print(mod)
   

   1.6666666666666667
   1
   1.0
   2

   • math module

     import math
     print(math.sin(3.14/4))
     

     0.706825181105366

3. Indexing operator

   See 2, the string of Section 9 .

4. Comparison operators, and logical operators

   symbol	DEFINITIONS
   ==（！=）	Determining whether the value of the variable is equal to two (not equal)
   is（is not）	Determining whether two variables refer to the same object (not the same)

   s1 = '100'
   s2 = str(100)
   print(s1 == s2)
   print(s1 is s2)      # s1 与 s2 引用的不是统一个字符串
   

   True
   False

   a = 30
   b = 27
   print(3**3<a and 5**2>b)
   print(3**3<a or 5**2>b)
   
   print(not 3**3<a)
   

   False
   True
   False

5. Ternary operator

   a = 20
   print('大于25') if a>25 else print('小于25')
   
   b = 25
   print('大于25') if b>25 else (print('等于25') if b==25 else print('小于25'))
   

   Less than 25
   equal to 25

   a = 30
   s = print('大于25'), '!' if a>25 else print('小于等于25')    # 多条语句用逗号隔开：每条语句都会执行，返回多条语句的返回值组成元祖
   print(s)      # print()没有返回值，因此返回 None
   

   Greater than 25
   (None, '!')

   a = 30
   s = print('大于25'); '!' if a>25 else print('小于等于25')    # 多条语句用分号隔开：每条语句都会执行，返回第一条语句的返回值
   print(s)      # print()没有返回值，因此返回 None
   

   Greater than 25
   None

6. in operator

   print('a' in 'abc')
   

   True