Python03 Object's Boolean program organization structure sequence structure selection structure single branch structure double branch structure multi branch structure nesting if Conditional expression pass sentence *range（） Use loop structure of function while loop for-in Flow control statement breakcontinueelse Statement nested loop in a double loop break and continue
Python Everything is an object , All objects have a Boolean value
Use built-in functions bool（） Gets the Boolean value of the object
# Boolean values of test objects
print(' The Boolean value of the following object is false')
print(bool(False)) # False
print(bool(0)) # False
print(bool(0.0)) # False
print(bool(None)) # False
print(bool('')) # False
print(bool("")) # False
print(bool([])) # An empty list False
print(bool(list())) # An empty list False
print(bool(tuple())) # An empty tuple False
print(bool({})) # An empty dictionary False
print(bool(dict())) # An empty dictionary False
print(bool(set())) # Empty set False
print(' Boolean values for other objects are True')
print(bool(18))
print(bool(1.1))
print(bool('hello'))# Sequential structure
''' Put the elephant in the fridge in a few steps '''
print('-------- Program starts ----------')
print('1. Open the refrigerator door ')
print('2. Put the elephant in the refrigerator ')
print('3. Close the refrigerator door ')
print('-------- Program end ----------')Single branch structure
money = 1000 # balance
s = int(input(' Please enter the withdrawal amount ')) # Withdrawal amount
# Judge whether the balance is sufficient
if money >= s:
money = money - s
print(' Successful withdrawals , The balance is ：', money)Two branch structure
# Two branch structure if...else, Choose one of the two
''' Enter an integer from the keyboard , Judge whether it's odd or even '''
num = int(input(' Please enter an integer '))
# conditional
if num % 2 == 0:
print(num, ' It's even ')
else:
print(num, ' Is odd ')Multi branch structure
# Multi branch structure , Select one more to execute
'''
Enter an integer from the keyboard , achievement
90-100 a
80-89 b
70-79 c
60-69 d
0-59 e
Less than 0 Or greater than 100 Illegal data
'''
score = int(input(' Please enter a grade '))
# Judge
if score >= 90 and score <=100:
print('A level ')
elif score >=80 and score <=89:
print('B level ')
elif 70 <= score <= 79:
print('C level ')
elif score >=60 and score <=69:
print('D level ')
elif score >=0 and score <=59:
print('E level ')
else:
print(' Illegal grades ')nesting if
''' members >=200 20 percent discount
>= 100 10% off
No discount
Non members >=200 5% off
No discount
'''
answer = input(" Are you a member ？y/n")
money = float(input(" Please enter your purchase amount "))
# If you are a member
if answer == 'y':# members
print(' members ')
if money >= 200:
print(" The payment amount ：", money*0.8)
elif money>=100:
print(" The payment amount ：", money * 0.9)
else:
print(" No discount , The payment amount ：", money)
else:
print(' Non members ')
if money >= 200:
print(" The payment amount ：", money*0.95)
else:
print(" No discount , The payment amount ：", money)Conditional expression
# Conditional expression
''' Enter two integers from the keyboard , Compare the size of two integers '''
num_a = int(input(' Please enter the first integer ：'))
num_b = int(input(' Please enter the second integer ：'))
# Compare the size
'''if num_a >= num_b:
print(num_a, ' Greater than or equal to ', num_b)
else:
print(num_a, ' Less than ', num_b)'''
print(' Use conditional expressions to compare ')
print(str(num_a) + ' Greater than or equal to ' + str(num_b) if num_a >= num_b else str(num_a) + ' Less than ' + str(num_b))pass sentence
pass Sentences do nothing , Just a placeholder , It's used where syntax requires statements
# pass sentence
answer = input(' Are you a member ？y/n')
# Judge whether you are a member
if answer == 'y':
pass
else:
passThe default starting value is 0
The default step size is 1
Built in functions range（）
Used to generate a sequence of integers
The return value is an iterator object
use in or not in Determine whether an integer exists
advantage ： No matter range How long is the sequence of integers represented by object , all range Objects take up the same amount of memory , Because you just need to store start,stop and step, Only when used range Object time , To calculate the relevant elements in the sequence
# range（） Three ways to create ''' The first way to create it , There is only one parameter （ Only one number is given in parentheses ） ''' r = range(10) # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9], The default from the 0 Start , Default phase difference 1 Step length print(r) # range(0,10) print(list(r)) # For viewing range Object -->list It means list ''' The second way to create , Give two parameters （ Give two numbers in parentheses ）''' r = range(1,10) # The starting value... Is specified , from 1 Start , To 10 end （ It doesn't contain 10）, The default step size is 1 print(r) # range(1, 10) print(list(r)) # [1, 2, 3, 4, 5, 6, 7, 8, 9] ''' The third way to create , Given three parameters （ Three parameters are given in parentheses ）''' r = range(1, 10, 2) print(list(r)) # [1, 3, 5, 7, 9] ''' Judge the specified integer , Whether there is... In the sequence , in , not in''' print(10 in r) # False ,10 Not in the current r In this sequence of integers print(9 in r) # True, 9 In the current r This sequence print(10 not in r) # True, 10 Not in the current r This sequence print(9 not in r) # False ,9 Not in the current r In this sequence of integers print(range(1, 20, 1)) print(range(1, 100, 1)) '''- No matter range How long is the sequence of integers represented by object , all range Objects take up the same amount of memory , Because you just need to store start,stop and step, Only when used range Object time , To calculate the relevant elements in the sequence '''
while loop
It is used to solve the cycle with an indefinite number of times
while Cycle and selection if The difference between ：if It's a judgment , Condition is True Do it once ;while Is a judgment n+1 Time , Condition is True perform n Time
Four step cycle method
1. Initialize variable 2. conditional 3. Conditional executors 4. Change variables
summary ： The initialized variable is the same as the conditional judgment variable and the changed variable
# Loop structure a = 1 # The expression of judgment condition while a < 10: # Execution condition executor print(a) a += 1
# Calculation 0-4 Cumulative sum between
''' The initialization variable is 0'''
a = 0
sum = 0 # Used to store cumulative sum
''' conditional '''
while a < 5:
''' Conditional executors （ The loop body ）'''
sum += a
a += 1
print(' And for ', sum)# Calculation 1-100 Between even numbers and
''' Initialize variable '''
a = 1
sum = 0 # Used to store even numbers and
''' conditional '''
while a <= 100:
''' Conditional executors （ The loop body ）'''
if not bool(a % 2):
sum += a
''' Change variables '''
a += 1
print("1-100 Between even numbers and ", sum)for-in
in Expression from （ character string 、 Sequence ） Take values in order , It's also called traversal
for-in The traversal object must be an iteratable object
Grammatical structure ：for Custom variables in Objects that can be iterated ：
The loop body
for item in 'Python': # The first time I took it out was P, take P assignment item, take item Value output of
print(item)
# range() Generate a sequence of integers --> It's also an iterative object
for i in range(10):
print(i)
# If you don't need to use custom variables in the loop body , You can set custom variables 1 Written as “_"
for _ in range(5):
print("i love python")
print(" Use for loop , Calculation 1-100 Between even numbers and ")
sum = 0 # Used to store even numbers and
for item in range(1, 101):
if item % 2 == 0:
sum += item
print('1-100 The even sum between is ：', sum)''' Output 100-999 Between the number of daffodils ''' for item in range(100,1000): ge = item % 10 shi = item // 10 % 10 bai = item //100 # print(bai, shi, ge) # Judge if ge**3+shi**3+bai**3 == item: print(item)
Flow control statement
break
Used to end the loop structure , Usually with branch structure if Use it together
''' Enter the password from the keyboard , Enter three times at most , If correct, end the loop '''
for item in range(3):
pwd = input(" Please input a password ：")
if pwd == "8888":
print(" The password is correct ")
break
else:
print(" Incorrect password ")
a = 0
while a < 3:
''' Conditional executors （ The loop body ）'''
pwd = input(" Please input a password ：")
if pwd == '8888':
print(' The password is correct ')
break
else:
print(' Incorrect password ')
''' Change variables '''
a += 1continue
Used to end the current loop , Enter next cycle , Usually associated with... In a branching structure if Use it together
''' Request output 1-50 There are many 5 Multiple '''
for item in range(1,51):
if item % 5 == 0:
print(item)
print('----------- Use continue-----------------')
for item in range(1,51):
if item % 5 != 0:
continue
else:
print(item)else sentence
if The conditional expression does not hold and should be executed else
for item in range(3):
pwd = input(" Please input a password ：")
if pwd == '999':
print(" The password is correct ")
break
else:
print(" Incorrect password ")
else:
print(' I'm sorry , The password was entered incorrectly three times ')stay while and for There is no break perform else
a = 0
while a < 3:
pwd = input(" Please input a password ：")
if pwd == "888":
print(" The password is correct ")
break
else:
print(' Incorrect password ')
# Change variables
a += 1
else:
print(' I'm sorry , The password was entered incorrectly three times ')Another complete loop structure is nested in the loop structure , The inner loop is executed as the loop body of the outer loop
''' Output a rectangle with three rows and four columns '''
for i in range(1,4):
for j in range(1,5):
print('*', end='\t') # Don't wrap output
print() # Line break ''' Output a multiplication table ''' for i in range(1,10): for j in range(1,i+1): print(i, '*', j, '=', i*j, end='\t') print()
In a double cycle break and continue
# Flow control statement ：break And continue Use in double cycle for i in range(5): # Represents the outer loop execution 5 Time for j in range(1,11): if j % 2 == 0: continue print(j, end='\t') print()
