1、语句格式
a. 简单的if语句
if conditional_test:
do something
b. if-else语句
if conditional_test:
do something
else:
do something
c. if-elif-else结构
if conditional_test:
do something
elif conditional_test:
do something
else:
do something
2、例子：
cars = ["audi", "bmw", "subaru","toyota"]
for car in cars:
if car == "bmw":
print(car.upper())
else:
print(car.title())
注意：a. if语句也是不用花括号；b. 用冒号
3、检查多个条件是用 and 和 or
age_1 >= 21 and age_2 >= 22
4、检查特定值是否在列表中
cars = ["audi", "bmw", "subaru","toyota"]
"bmw" in cars / "bmw" not in cars 可以用来判断这个值是不是在列表中