Learning Diary for Python - 4

One 、 Ternary operator

1、C Language

• expression - ? value 1: value 2
• Operation rules ： If the expression is true , The result of the operation is the value 1, Otherwise it's worth 2

2、python

• expression - value 1 if expression 1 else value 2

• Operation rules ： If the result of the expression is True, Result is value 1, Otherwise it's worth 2.

  # Example ：
  #1
  a=100
  result=1 if a>100 else 0
  print(result)
  #2
  a=100
  a+=1 if a>10 else -1
  print(a)
  #3
  a=100
  a=a+1 if a>10 else a-1# The value can be an operator 
  print(a)
  

Two 、while loop

1、 grammar

# Format ：
while Conditional statements ：
The loop body
Other code

Noun function while keyword ; Fixed writing Conditional statements An expression with a result （ Except assignment statements ）： Fixed writing The loop body And while One or more statements that hold an indent ; Code that will be executed repeatedly

2、 Operation rules

First, judge whether the conditional statement is True, If so, execute the loop body ; Judge and execute after execution , Until the result of the conditional statement is False

3、 How to use it

# loop 5 Time 
times=0
while times<5
print(' loop ')
n+=1
# Infinite loop 
while True:
print(' loop ')

4、for And while Usage choice

• The number of cycles determines the use of for; Not sure to use while
• for Problems that cannot be solved can be reused while

# Login system 
acount={
"acount1":"123","acount2":"234","acount3":"345"}
while True:
name =input (' Please enter a user name ：')
if name in acount:
break
else:
print(' The username does not exist ')
while True:
password = input (' Input password ：')
if acount[name] == password:
print(' Get into ')
break
else:
print(' Wrong password ')
continue

3、 ... and 、 Circular keyword

1、continue

• usage ： End a cycle （ End the current cycle ）

2、break

• usage ： End the cycle

  # Guess number games 
  import random# Import random modular 
  my_num = random.randint(1, 100)# Produce a 1 To 100（ Closed interval ） The random number .
  times = 1
  while True:
  print(f' Start the first {
  times} Guess the number ')
  you_num = input(" Please enter an integer (1-100):")
  if you_num=='':
  continue
  you_num = int(you_num)
  if not 0<you_num<=100:
  continue
  if my_num == you_num:
  print(f' Congratulations on your guesses , The number is {
  my_num}')
  break
  else:
  if my_num > you_num:
  print(' The number is small ')
  else:
  print(' The number is too big ')
  times += 1
  

3、else keyword

• Complete cycle structure

  • complete for：

    for Variable in Sequence ：
    The loop body
    else：
    Code segment
    

  • complete while：

    while Conditional statements ：
    The loop body
    else：
    Code segment
    

  • About else：

    • else The existence of does not affect the execution of the original loop
    • Cyclic Division break Execute at the end of the else Code snippet after

    # Determine whether the string is a stored numeric string 
    # Method 1 
    str='123456789ab123'
    for x in str1:
    if not '0' <= x <= '9':
    print(str1, ' It's not a pure numeric string ')
    break
    else:
    print(str1, ' Is a pure numeric string ')
    # Method 2 
    str1 = '123456789ab123'
    flag = True
    for x in str1:
    if not '0' <= x <= '9':
    flag = False
    break
    if flag:
    print(' Pure numeric string ')