【Python if语句】形式与条件控制操作示例

if 语句文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/11216.html

Python中if语句的一般形式如下所示：文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/11216.html

if condition_1:
  statement_block_1
elif condition_2:
  statement_block_2
else:
  statement_block_3

如果 "condition_1" 为 True 将执行 "statement_block_1" 块语句，如果 "condition_1" 为False，将判断 "condition_2"，如果"condition_2" 为 True 将执行 "statement_block_2" 块语句，如果 "condition_2" 为False，将执行"statement_block_3"块语句。文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/11216.html

Python中用elif代替了else if，所以if语句的关键字为：if – elif – else。文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/11216.html

注意：文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/11216.html

1、每个条件后面要使用冒号（:），表示接下来是满足条件后要执行的语句块。文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/11216.html

2、使用缩进来划分语句块，相同缩进数的语句在一起组成一个语句块。文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/11216.html

3、在Python中没有switch – case语句。文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/11216.html

以下实例演示了狗的年龄计算判断：文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/11216.html

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>')

将以上脚本保存在文件中，并执行该脚本：文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/11216.html

python
Age of the dog: 1
about 14 human years文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/11216.html

以下为if中常用的操作运算符:文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/11216.html

# 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)

以上实例输出结果：文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/11216.html

False
False文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/11216.html

high_low.py文件：文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/11216.html

#!/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.")