Chapter 3: Input functions and operators in Python

1. The input function input() in Python

• Introduction to the input() function

• Basic use of input() function

• code demo

  • code writing

  # 输入函数input()
  present = input("你想要什么礼物呢？")
  print(present, type(present))
  

  • Result analysis

  你想要什么礼物呢？巧克力
  巧克力 <class 'str'>
  

2. Operators in Python

• Common Operators in Python

2.1 Arithmetic operators

2.1.1 Arithmetic operators

standard arithmetic operators	Add (+), Subtract (-), Multiply (*), Divide (/), Divide evenly (/)
remainder operator / modulo operator	%
exponentiation operator	******

• code demo

  • code writing

  print(1 + 1)  # 加法运算
  print(1 - 1)  # 减法运算
  print(2 * 4)  # 乘法运算
  print(11 / 2)  # 除法运算
  print(11 // 2)  # 整除运算
  
  print(11 % 2)  # 取余运算（取模运算）
  
  print(2 ** 3)  # 幂运算，表示的是2的三次方
  

2.1.2 Operation rules

In the operation of remainder and integer division, special attention should be paid to follow the formula when the operation data is one positive and one negative

Take the remainder (one positive and one negative), the formula for taking the remainder: remainder = dividend - divisor * quotient ; to divide two numbers, the dividend is divided by the divisor

Divisibility (one positive and one negative), the formula for divisibility: round down **

operator	express	example	result
+	add	1+1	2
-	reduce	1-1	0
*	take	2*4	8
/	remove	1/2	0.5
%	Remainder (full positive)	9%4	2
	remainder (all negative)	-9%-4	2
	Take the remainder (one positive and one negative), the formula for taking the remainder: remainder = dividend - divisor * quotient; to divide two numbers, the dividend is divided by the divisor	-9%4	-3
**	exponentiation	2**3	8
//	Evenly divisible (all positive), take the quotient value	11/2	5
	divisible (all negative)	-11/-2	5
	Divisibility (one positive and one negative), divisive formula: round down	-9 // 4	-3

• code demo

  • code writing

  # 一整一负的整除和取余运算
  print(9 // 4)  # 2
  print(-9 // -4)  # 2
  # 整除运算，取商值
  
  print(9 // -4)  # -3
  print(-9 // 4)  # -3
  # 一正一负，整除公式：向下取整
  
  print(9 % -4)   # -3=9-(-4)*(-3）
  print(-9 % 4)   # 3=-9-(4)*(-3)
  # 一正一负，取余公式：余数=被除数-除数*商；两数相除，被除数 除以 除数
  

2.2 Assignment operator

• Assignment operator symbol: =

• Execution order: right --> left

• Support chain assignment : a=b=c=20

• Support parameter assignment : +=, -=, *=, /=, //=, %=

• Support series unpacking assignment : a,b,c=20,30,40

• code analysis

  • code writing

  i = 3 + 4
  print(i)  # 7
  print("--------------链式赋值---------------")
  a = b = c = 20  # 链式赋值
  print(a, id(a))  # 20 2474963921808
  print(b, id(b))  # 20 2474963921808
  print(c, id(c))  # 20 2474963921808
  
  print("--------------支持参数赋值---------------")
  a = 20
  a += 30  # 相当于a=a+30
  print(a)  # 50
  a -= 10  # 相当于a=a-10
  print(a)  # 40
  a *= 10  # 相当于a=a*10
  print(a, type(a))  # 400< class 'int'>
  a /= 10  # 相当于a=a/10
  print(a, type(a))  # 40.0 <class 'float'>
  
  print("--------------支持系列解包赋值---------------")
  a, b, c = 20, 30, 40
  print(a, b, c)  # 20 30 40
  
  print("--------------交换两个对象的值---------------")
  a, b = 10, 20
  print("交换前a和b的值", a, b)  # 交换前a和b的值 10 20
  # 交换
  a, b = b, a
  print("交换后a和b的值", a, b)  # 交换后a和b的值 20 10
  

2.3. Comparison Operators

• Comparison operators: compare the results of variables or expressions in terms of size , true or false, etc.

2.3.1 Comparison operators

comparison operator
< > >= <= !=
==	Comparison of object values
is is not	Comparison of object ids

• code demo

  • code writing

  a, b = 10, 20
  print("a>b吗？", a > b)  # False
  print("a>b吗？", a < b)  # True
  

2.3.2 == and =

• A = becomes the assignment operator

• Two == are called comparison operators

• A variable consists of three parts, identification (id), type (type), value (value)

• == compares the value of the object (value)

• The identity (id) of the comparison object

• code demo

  • code writing

  a = 10
  b = 10
  print(a == b)  # True 说明a和b的值value相等
  print(a is b)  # True 说明a与b的标识id相等
  print(a is not b)  # False,a的id和b的id不相等
  
  lst1 = [11, 22, 33, 44]
  lst2 = [11, 22, 33, 44]
  print(lst1 == lst2)  # True
  print(lst1 is lst2)  # False
  print(id(lst1))  # 1810724741952
  print(id(lst2))  # 1810733359616
  print(lst1 is not lst2)  # True
  

2.4. Boolean operators

2.4.1 Illustration of Boolean operators

operator	Operand 1	Operand 2	operation result	Remark
and	True	True	True	The result of the operation is True only if both operands are True
	True	False	False
	False	True	False
	False	False	False
or	True	True	True	As long as one of the operands is True, the result of the operation is True
	True	False	True
	False	True	True
	False	False	False
not	True		False	If the operand is True, the result of the operation is False
	False		True	If the operand is False, the result of the operation is True

• code demo

  • code writing

  a, b = 1, 2
  print("----------and 并且-------------")
  print(a == 1 and b == 2)  # True
  print(a == 1 and b < 2)  # False
  print(a != 1 and b == 2)  # False
  print(a != 1 and b != 2)  # False
  
  print("----------or 或者-------------")
  print(a == 1 or b == 2)  # True
  print(a == 1 or b < 2)  # True
  print(a != 1 or b == 2)  # True
  print(a != 1 or b != 2)  # False
  
  print("----------not 取反-------------")
  f = True
  f2 = False
  print(not f)  # False 
  print(not f2)  # True
  
  print("----------in 和 not in-------------")
  s = "hello world"
  print("w" in s)  # True
  print("w" not in s)  # False
  print("u" in s)  # False
  print("u" not in s)  # True
  

2.5 Bitwise operators

• Bit operator: convert data into binary for calculation

2.5.1 Illustration of bitwise operators

operator	significance	Calculation
&	bitwise AND operation	The corresponding digits are all 1, the result digit is 1, otherwise it is 0
|	bitwise OR operation	The corresponding digits are all 1, the result digit is 1, otherwise it is 0
<<	left shift operator	The high bit overflow is discarded, and the low bit is filled with 0
>>	right shift operator	The lower bit overflows and is discarded, and the higher bit is filled with 0

3. Operator precedence

• Operation Priority Icon

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