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2、 Operators and branches
2022-07-04 10:38:00 【She was your flaw】
Operators and branches
Operators are divided into : Numeric operators 、 Comparison operator 、 Logical operators 、 Assignment operator
One 、 Mathematical operators :+( Add )、-( reduce )、*( ride )、/( except )、%( Mod 、 modulus )、//( to be divisible by )、**( Power operation )
- +、-、*、/ And in mathematics +、-、×、÷ The function is as like as two peas
print(5 + 2) # 7
print(5 - 2) # 3
print(5 * 2) # 10
print(5 / 2) # 2.5
- % - Mod 、 modulus
x % y — seek x Divide y The remainder of
application 1: Judge whether a number can be divided by another number ( See if the remainder is 0)
print(5 % 2) # 1
print(16 % 2) # 0
print(15 % 5) # 0
application 2: Take the lower digits ( Yes 10 perhaps 10 To the power of )
num = 2398
print(num % 10) # 8
print(num % 100) # 98
num = 4621
print(num % 2) # 1
print(num % 10) # 1
print(num % 20) # 1
print(num % 100) # 21
- // - to be divisible by
x // y - x Divide y The quotient of is rounded to the small
print(5 // 2) # 2; 2 2.5 3
print(1.8 // 2) # 0.0; 0 0.9 1
print(-5 // 2) # -3; -3 -2.5 -2
application : Positive integer to low
num = 23489
print(num // 10) # 2348
print(num // 100) # 234
# practice 2: Gets the tens of the specified positive integer
num = 3945
print(num // 10 % 10) # 4
print(num % 100 // 10) # 4
# practice 3: Get the hundreds of the specified positive integer
num = 3945
print(num // 100 % 10) # 9
print(num % 1000 // 100) # 9
- ** - Power operation
x ** y - seek x Of y Power
print(2 ** 3) # 8
print(5 ** 3) # 125
print(16 ** 0.5) # 4.0
print(27 ** (1/3)) # 3.0
print(2.2 ** 2) # 2.2 * 2.2 = 4.84
print(2.0 ** 2) # 4.0
Two 、 Comparison operator :==( be equal to )、!=( It's not equal to )
Important conclusions : The result of all comparison operations is Boolean
print(10 > 20) # False ( wrong )
print(10 >= 10) # True ( Yes )
print(20 != 10) # True ( Yes )
Be careful :python The comparison operator in can express the range through concatenation like data
age = 16
print(18 <= age <= 28)
3、 ... and 、 Logical operators :and( Logic and operators )、or( Logic or operation )、not( Logic is not )
1.and - Logic and operators
(1) Application scenarios : Equivalent to life and , Used to connect multiple conditions that need to be met at the same time
(2) Operational rules : All two are True The result is True, As long as one is False The result is False
# Conditions 1 and Conditions 2
True and True - True
True and False - False
False and True - False
False and False - False
practice : Write a number that can be simultaneously 3 and 7 The condition of division
num = 67
# Conditions 1: Can be 3 to be divisible by - num % 3 == 0
# Conditions 2: Can be 7 to be divisible by - num % 7 == 0
print(' Whether it can be 3 and 7 to be divisible by :'num % 7==0) and print(num % 3==0) # False
print(' Whether it can be 3 and 7 to be divisible by :'num % 21==0) # False
2.or - Logic or operation
(1) Application scenarios : Equivalent to or in life , It is used when one of the conditions needs to be met
(2) Operational rules : As long as one is True The result is True, All two are False The result is False
# Conditions 1 and Conditions 2
True or True - True
True or False - True
False or True - True
False or False - False
gpa = 4.0
score = 95
# Conditions for scholarship : Grade point higher than 4 Or the score of gymnastics is not lower than 95
# Grade point higher than 4: gpa > 4
# The score of gymnastics is not lower than 95: score >= 95
print(' Can I get a scholarship :', gpa > 4 or score >= 95) # True
practice : Judge whether the specified year is a leap year
# Common leap year : Can be 4 Divisible but not by 100 to be divisible by : year % 4 == 0 and year % 100 != 0
# Leap year of the century : Can be 400 to be divisible by : year % 400 == 0
# Can be 4 to be divisible by : year % 4 == 0
# Can not be 100 to be divisible by : year % 100 != 0
# Can be 400 to be divisible by : year % 400 == 0
year = int(input(' Please enter the year :')) # perhaps year = 2020
print(' Is it a leap year :',(year % 4 == 0 and year % 100 != 0) or year % 400 == 0)
- not - Logic is not
not Conditions - A negative condition
(1) Application scenarios : Negate the specified condition ( Take the opposite ). Generally used for positive conditions, there are many complex situations , When the reverse condition is simple , Conditions are written backwards and then added not
(2) Operational rules : True change False, False change True
not True - False
not False - True
# Older than 18: age > 18
# Be no older than 18: age <= 18、 not age > 18
num = 18
print(num == 18)
print(not num == 18, num != 18)
# practice : Write one that cannot be 3 and 7 The condition of division
# Can be 3 Division cannot be 7 to be divisible by
# Can be 7 Division cannot be 3 to be divisible by
# Can neither be 3 It can't be divided 7 to be divisible by
print(not num % 21 == 0)
4. Short circuit operation
# Conditions 1 and Conditions 2 --- If the condition 1 yes False, So the conditions 2 Not execute
# Conditions 1 or Conditions 2 --- If the condition 1 yes True, So the conditions 2 Not execute
True and print(' And the condition of operation 2') # Both conditions are met
False and print(' And the condition of operation 2') # Conditions 1 dissatisfaction , Direct negation
False or print(' Or the condition of operation 2') # Conditions 1 dissatisfaction , Conditions 2 Satisfy , Choose the conditions 2( If the condition 1 Satisfy , You don't have to look at the conditions 2 Is it true )
- Extension of logical operators - The operand is not a Boolean
data 1 and data 2 - If data 1 The Boolean value of is True, The result is data 2, Otherwise, the result is data 1
data 1 or data 2 - If data 1 The Boolean value of is True, The result is data 1, Otherwise, the result is data 2
print(8 and 7) # 7
print(10 and 7) # 7
print(0 and 7) # 0
print(False and 7) # False
print(8 or 7) # 8
print(0 or 7) # 7
- Boolean value of data - The result of converting data to Boolean ( Of particular importance )
python All types of data in have Boolean values .
All Boolean values corresponding to zero and null values are False, The Boolean values of other data are True.
Common zero and null values : 0、0.0、0.00、’’、""、[]、()、{}、None.
print(bool(0), bool(0.0), bool('')) # False False False
print(bool(12), bool(-9.454), bool('ban')) # True True True
Four 、 Assignment operator :=、+=、*=、/=、%=、//=、**=
( important !) Important conclusions : The function of all assignment operations is to assign values to variables , Will not produce a result .( The expression of assignment operation has no result )
The left side of all assignment operators must be variables
a = 10
10 > 20
# print(a = 10) # Report errors
print(10 > 20)
- =
Use when defining variables or re assigning values to variables
name = 20
num = 10 * 20
2.=、+=、*=、/=、%=、//=、**=
requirement : The variable before the assignment symbol must be a defined variable
Variable += data --- Variable = Variable + data
b = 10
b += 2
print(b) # 12
b -= 3
print(b) # 9
b **= 2
print(b) # 81
b %= 2
print(b) # 1
3. Operator precedence
Mathematical operators > Comparison operator > Logical operators > Assignment operator
# Mathematical operators : ** > * , / , % , // > + , -
# If there are brackets, count the... In the brackets first
b = 10 + 30
c = 10 < 5 * 3 # First calculate c = 10<15 Count again c = True
print(c) # True
Branching structure
1. Process control
1) Sequential structure ( Default ) - The code is executed from top to bottom , Each statement is executed once ;
2) Branching structure - The execution of the code depends on whether the condition is true (if sentence );
3) Loop structure - Let the code repeat (for,while).
print('1') # 1
print('2') # 2
print('3') # 3
2.if Branching structure
(1) if Single branch structure - Perform an operation when conditions are met , If this condition is not satisfied, the operation will not be executed .
a. grammar :
if Conditional statements :
Code segment
b. explain
if - keyword , Fixed writing .
Conditional statements - Any expression with a result , for example : data , Operation expression ( Except assignment ), Function call expression, etc .
: - Fixed writing .
Code segment - That's right. if One or more statements that hold an indent ( At least one ); It is necessary to meet the conditions before executing the code .
c. Execution process
First, judge whether the conditional statement is True( If the result of a conditional statement is not Boolean , Just turn it into Boolean and see ), If True Just execute the code snippet , Otherwise, the code segment will not execute .
a = 100
if a > 10:
print(' Code 1') # Code 1
print(' Code 2') # Code 2
print(' Code 3') # Code 3
print(' Code 4') # Code 4
# practice : If the specified number is even, print ' even numbers '
num = 23
if num % 2 == 0:
print(' even numbers ')
if not num % 2:
print(' even numbers ')
# If the specified number is odd, print ' Odd number '
if num % 2 == 1:
print('646464') # 646464
num = 153
a = num % 10
b = num // 10 % 10
c = num // 100
if a**3 + b**3 + c**3 == num:
print(' This number is narcissus number ') # This number is narcissus number
(2) if Two branch structure - Perform an operation when conditions are met , When this condition is not satisfied, perform another operation
grammar :
''' if Conditional statements : Code segment 1 else: Code segment 2 '''
num = 30
if 220 > num:
print(123) # 123
else:
print(321)
age = 12
if age >= 18:
print(' adult ')
else:
print(' The child ') # The child
(3) if Multi branch structure - Do different things according to different conditions
if - elif - elif - … - else
''' if Conditional statements 1: Code segment 1 elif Conditional statements : Code segment 2 elif Conditional statements 3: Code segment three . . . else: Code segment N '''
score = 98
if 60 > score:
print(' Bad ')
elif score < 80:
print(' commonly ')
elif score < 90:
print(' good ')
# elif score <= 100:
else:
print(' optimal ') # optimal
choice question
print(100 - 25 * 3 % 4)
What should be output ? (B)A. 1
B. 97
C. 25
D. 0
Which of the following statements is wrong (A).
A. Except for dictionary types , All standard objects can ⽤ Yu Boolean test
B. The Boolean value of an empty string is False
C. The Boolean value of an empty list object is False
D. The value is 0 The Boolean value of any numeric object of is False
The value of the following expression is True Yes. (B).
A. 3>2>2
B. 1 and 2 != 1
C. not(11 and 0 != 2)
D. 10 < 20 and 10 < 5
Python No ⽀ The data types held are (A).
A. char
B. int
C. float
D. list
( multi-select )n = 6784, You can get 7 Of ⽅ FA you (C、D).
A. n / 1000 % 100
B. n % 1000 / 100
C. n // 100 % 10
D. n // 10 % 100 // 10
shipment ⾏ The following procedure , When typing from the keyboard ⼊12, shipment ⾏ The result is (A).
x = (input()) print(type(x))
A. <class 'str'>
B. <class 'int'>
C. error
D. <class 'dict'>
The operation result of the following expression is (D ) .
a = 100 b = False print(a * b > -1)
A. False
B. 1
C. 0
D. True
Completion
- The function name to view the type of data in the variable is (type()).
- It is known that x = 3 == 3 , Of board ⾏ After the end , Variable x The value of is (True).
- It is known that x = 3 , So clinging ⾏ sentence x += 6 after ,x The value of is (9).
- expression 3 ** 2 The value of is (9), expression 3 * 2 The value of is (6), expression 4 ** 0.5 The value of is (2.0).
Programming questions
Write a judgment ⼀ Whether the number can be at the same time 2 and 5 Divisible conditional statement , And print the corresponding results .
q = 16 print(q % 2 == 0 and q % 5 == 0) # False
Write a judgment ⼀ Whether the number can be 2 perhaps 5 to be divisible by , But not both 2 perhaps 5 Divisible conditional statement , And print the corresponding results .
q = 35 input((q % 2 == 0 or q % 5 == 0)and q % 10 != 0) # True
Suppose today's class time is 15678 second , Program to calculate the class time today ⼩ when , How many minutes? , How many seconds ; With ‘XX
when XX branch XX second ’ Of ⽅ Express .
for example :100 Seconds are expressed as 0 when 1 branch 40 second
time=15678 a=time // 3600 b=(time - a*3600) // 60 c=time - a * 3600 - b * 60 print(a,' when ',b,' branch ',c,' second ') # 4 when 21 branch 18 second
Define two variables to save ⼀ individual ⼈ Body ⾼ And weight , The programming implementation judges this ⼈ Is your figure normal !
The formula : weight (kg) / ( body ⾼(m) The level of ⽅ value ) stay 18.5 ~ 24.9 It's normal .
Output format : If there is something wrong :True/False
# weight = 47kg height = 1.65 if 18.5 <= 47 / (1.65 ** 2) <= 24.9: print(' normal ') else: print(' Is not normal ') # Is not normal
Print according to the range of grades entered
pass
perhapsfail,
a = 80 if a >=60: print(' pass ') else: print(' fail, ') # pass
Print according to the entered age range
adult
perhapsA minor
, If the age is not within the normal range (0~150) PrintThis is not a person !
.age = int(input(' Please enter age ')) if 18 <= age <= 150: print(' adult ') elif 0 < age < 18: print(' A minor ') else: print(' This is not a person ')
Enter two integers a and b, if a-b The result is an odd number , The result is output , Otherwise, the prompt message will be output
a-b The result is not an odd number
.a = 67 b = 24 if (a - b) % 2==1: print(a - b,' Is odd ') else: print(a-b, ' It's not an odd number ') # 43 Is odd
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