Python学习-Chapter5 if语句

cars = ['audi','bmw','subaru','toyota']

for car in cars:
    if car == 'bmw':
      print (car.upper())
    else:
      print(car.title())

Audi
BMW
Subaru
Toyota

my_name = 'oliver'

print(my_name == 'oliver')

print(my_name == 'taylor')

True
False

cars = ['aUdi','bMw','sUBaru','tOYota']
print(cars[0] == 'audi')

print('忽略大小写后，进行四个元素的遍历检查')

for car in cars:  #用for注意冒号和缩进！
  print(car.lower() == 'bmw')

print(cars)

False
忽略大小写后，进行四个元素的遍历检查
False
True
False
False
['aUdi', 'bMw', 'sUBaru', 'tOYota']

cars = ['audi','bmw','subaru','toyota']

check = 'bmw' in cars

print(check)

True

语法：

if 条件:
  执行块
else:
  执行块
#注意缩进 和 冒号！！！  有缩进的默认在执行块内

语法：

if 条件1:
  执行块
    
elif 条件2:
  执行块
    
else:
  执行块
    
    #注意：如果if通过，elif 和 else 全部跳过
        # if 没过 elif过了，else跳过
        # 其余情况都是else

#当if语句中输出字符串出现重复，简化代码小技巧：
#eg：
age = 12

if age<14:
    print("your admission cost is $0.")
elif age<18:
    print("your admission cost is $25.")
else:
    print("your admission cost is $40.")

your admission cost is $0.

#利用f字符串进行简化：
age = 12

if age<14:
   price = 0
elif age<18:
   price = 25
else:
   price = 40
    
print(f"your admission cost is ${price}.")

your admission cost is 0$.

age = 38
if age<4:
   price = 0

elif age<18:
   price = 25

elif age<65:
   price = 40

else:  #最后不一定用else结尾，这个可以写成elif
   price = 20
    
print(f"your admission cost is ${price}.")

your admission cost is $40.

cars = ['audi','bmw','subaru','toyota']
for car in cars:
  if car == 'bmw':
    print(f"My favorite car is {car}")

My favorite car is bmw

cars = []
if cars:   #if 列表：  列表为空就为false，反之为true。
    print("cars")
else:
    print("there is no car in your carlist.")

there is no car in your carlist.

cars = ['audi','bmw','subaru','toyota']
afordable_cars = ['audi','toyota']
for car in cars:
    if car in afordable_cars:
      print(f"The {car} you love is afordable.")#注意缩进
    else:
      print(f"You can't buy {car} you love right now.")#注意这里else和上面的if对齐

The audi you love is afordable.
You can't buy bmw you love right now.
You can't buy subaru you love right now.
The toyota you love is afordable.