1. if condition statement
if conditions: Code block - true execution else: optional Code block condition is false execution
n = int(input('Please enter a number:')) if n > 0: print('%s Greater than 0' % n) else: print('%s Less than 0' % n)
The if statement supports nesting:
if conditions: if conditions: Code block else: Code block else: Code block
if - elif - else
When there are multiple conditions, it is not so convenient to always use if to judge. In order to be lazy, we introduced elif, the abbreviation of if - else.
score = int(input('Please enter a score:')) if 100 >= score >= 90: print('A') if 90 > score >= 80: print('B') if 80 > score >= 60: print('C') if 60 > score >= 0: print('D') if score < 0 or score > 100: print('Input error')
score = int(input('Please enter a score:')) if 100 >= score >= 90: print('A') elif 90 > score >= 80: print('B') elif 80 > score >= 60: print('C') elif 60 > score >= 0: print('D') else: print('Input error')
2. while loop statement
If the condition is true, the loop body always executes.
while condition: Circulatory body
while True: print('Dead cycle')
count = 0 while count < 10: # count less than 10, loop until it is greater than 10, exit loop print('hello') count += 1 print('ok')
The while loop statement can also have else's identity:
number = 23 running = True while running: guess = int(input('enter a integer: ')) if guess == number: print('congratulations,you guessed it!') print('but,you do not win any prizes!') running = False # Loop ends here, jumps out of loop, and executes else elif guess < number: print('no,it is a litter higher than that') else: print('no, it is a litter lower than that') else: print('The while loop is over') print('Done!')
3. for loop statement
for i in 'she': print(i) s h e
The range ([start,] stop [, step = 1]) function can be used to create a list of integers, which is often used with for statements.
>>> s = range(5) # Generate a list of integers 0 - 5 >>> type(s) <class 'range'> >>> list(s) [0, 1, 2, 3, 4] for i in range(3): print(i) 0 1 2
4. break statement
The function of break statement is to terminate the loop and exit the loop.
n = 0 while n < 10: n += 1 if n % 2 == 0: # Exit loop when n = 2 break print(n) 1
5. continue statement
The continue statement is used to terminate this cycle, continue the next cycle, and determine the cycle conditions before the next cycle.
n = 0 while n < 10: n += 1 if n % 2 == 0: # When n is even, terminate this cycle and continue the next cycle break print(n) 1，3，5,7,9
6. exercise questions
n = 1 while n < 11: if n == 7: pass else: print(n) n += 1
2. Calculate the sum of 1 - 100
n = 1 sum = 0 while n < 101: sum += n n += 1 print(n)
3. Calculate the sum of 1-2 + 3-4 + 5-6... 99
n = 1 sum = 0 while n < 100: temp = n % 2 if temp == 0: sum -= n else: sum += n n += 1 print(sum)
4. Calculate the sum of all even numbers 1-100
n = 1 while n < 101: if n % 2 == 0: sum += n else: pass # pass means that the code is not executed. n += 1 print(sum)
5. User login (three retries)
count = 0 while count < 3: user = input('Please enter your user name:') psd = input('Please enter your password:') if user == 'Alina' and psd == '123456': print('Welcome back %s' % user) else: print('Input error, please try again') count += 1