【Python编程：从入门到实践】IF语句

IF语句

• < <= >= > != ==
• 检查多个条件
• • and 都true为true，有假即假，左边假右边的不计算
• • or 有真即真，左真则右边不计算
• 检查特定值
• • in 检查特定值是否在列表中，在返回值True
• • not in 检查特定值是否不在列表中，不在返回True
• if语句
• • if …
• • if … else …
• • if … elif … else …
• • if … elif … elif … else …满足一个if或elif则后面的不再执行
• • if … elif … elif …
• • 多条件

5.1 a demo_1

names = ['Bob','Lucy','Mary','Lisa']
for name in names:
    if name.lower()=='lucy':
        print(name.upper())
    else:
        print(name.lower())
#bob
#LUCY
#mary
#lisa

5.2 检查特定值是否在/不在列表中

names = ['Bob','Lucy','Mary','Lisa']
print('Bob' in names) #True
print('bob' not in names)#True

5.3 布尔表达式

bl = True
if bl:
    print('bl is '+str(bl))
    #bl is True

5.4 a demo_2

cars = ['audi','bmw','subaru','toyota']
for car in cars:
    if car == 'subaru':
        print("is car == 'subaru'?t predict True")
        print(car == 'subaru')
        #is car == 'subaru'?t predict True
        #True

5.5 a demo_3

car = 'AUDI'
cars = ['audi','bmw','subaru','toyota']
for car_ in cars:
    if car.lower()==car_:
        print(car.lower()==car_)

5.6 顾客加菜

client_menu = ['Leeks','Garlic',' Shrimp','Salmon']
client_request = ['cabbage','cucumber','lettuce','perilla']
if 'cabbage' in client_request:
    client_menu.append('cabbage')
if  'cucumber' in client_request:
    client_menu.append('cucumber')
if 'perilla' in client_request:
    client_menu.append('perilla')
print(client_menu)
#['Leeks', 'Garlic', ' Shrimp', 'Salmon', 'cabbage', 'cucumber', 'perilla']

5.7 年龄分级

age = 60
if age < 2:
    print('婴儿')
elif 2 <= age and age < 4:
    print("蹒跚学步")
elif 4 <= age and age < 13:
    print("儿童")
elif 13 <= age and age < 18:
    print("青少年")
elif 18 <= age and age < 60:
    print("成年人")
elif age >= 60:
    print("老年人")

5.8 序数列表

lists = [i for i in range(1,10)]
if lists:
    for num in lists:
        if num == 1:
            print(str(num)+"st")
        elif num == 2:
            print(str(num)+"nd")#前面都不满足，此项才执行
        elif num == 3:
            print(str(num)+"rd")#前面都不满足，此项才执行
        else:
            print(str(num)+"th")#前面都不满足，此项才执行