Python3 condition control

The general form of an if statement in Python is as follows:

if condition_1:
    statement_block_1
elif condition_2:
    statement_block_2
else:
    statement_block_3

If "condition_1" is True, the "statement_block_1" block statement is executed, if "condition_1" is False, "condition_2" is judged, and if "condition_2" is True, the "statement_block_2" block statement is executed, and if "condition_2" is False, the statement is executed _block_3" block statement.

The eelse if is replaced by elif in Python, so the keyword for the if statement is: if - elif - else.

Attention:

• 1, each condition is followed by a colon (:), indicating that the next is to meet the condition after the statement block to be executed.
• 2, the use of indentation to divide the statement block, the same indentation of the statement together to form a statement block.
• 3. There is no switch-case statement in Python.

Instance

The following example demonstrates the age calculation of a dog:

age = int(input("Age of the dog: "))
print()
if age < 0:  
    print("This can hardly be true!") 
elif age == 1:  
    print("about 14 human years") 
elif age == 2:  
    print("about 22 human years") 
elif age > 2:
  human = 22 + (age -2)*5
  print("Human years: ", human)

### 
input('press Return>')

Save the above script in dog.py file and execute the script:

python dog.py
Age of the dog: 1

about 14 human years

Here are the operators commonly used in if:

Instance

# 程序演示了 == 操作符
# 使用数字
print(5 == 6)
# 使用变量
x = 5
y = 8
print(x == y)

The above example output results:

False
False

high_low.py file:

#!/usr/bin/python3 
# 该实例演示了数字猜谜游戏
number = 7
guess = -1
print("Guess the number!")
while guess != number:
    guess = int(input("Is it... "))
 
    if guess == number:
        print("Hooray! You guessed it right!")
    elif guess < number:         print("It's bigger...")     elif guess > number:
        print("It's not so big.")