python基础（四）

4.if语句

#一个简单示例

letters = ['aa','bb','cc','dd','ee']
for letter in letters:
    if letter == 'cc':
        print(letter.upper())
    else:
        print(letter.title())

Aa
Bb
CC
Dd
Ee

#条件测试

haha = 'jingjing'

if haha != 'jingjian':
    print("wrong!")

wrong!

#检查多个条件
age_0 = 22
age_1 = 18
age_0 >= 21 and age_1 >= 21

False

age_0 >= 21 or age_1 >= 21

True

(age_0 >= 21) and (age_1 <= 21)

True

#检查特定值是否包含在列表中
dd = ['yu','li','lu','ting']
'jing' in dd

False

'ting' in dd

True

if 'lu' not in dd:
    print("buzai")
else:
    print("zai")

zai

#布尔表达式，条件测试的别名，结果是Ture或者False
game_active = Ture
can_edit = False

#if语句

#if elif else
age = 10
if age < 4:
    print('free')
elif age < 18:
    print('5')
else:
    print('10')

5

age = 36
if age < 4:
    print('free')
elif age < 18:
    print('5')
else:
    print('10')

10

age = 36
if age < 4:
    price = 0
elif age < 18:
    price = 5
elif age < 65:
    price = 10
else:
    price = 0
print("cost is:" + str(price)+ "!")

cost is:10!

#省略else部分
age = 69
if age < 4:
    price = 0
elif age < 18:
    price = 5
elif age < 65:
    price = 10
elif age > 65:
    price = 0
print("cost is:" + str(price)+ "!")

cost is:0!
#使用if语句处理列表

letters = ['a','b','c','d','e']
for letter in letters:
    print("adding " + letter + ".")
print("
Ok!")

adding a.
adding b.
adding c.
adding d.
adding e.

Ok!

letters = ['a','b','c','d','e']
for letter in letters:
    if letter =='c':
        print('yeyey')
    else:
        print('nonon')

nonon
nonon
yeyey
nonon
nonon

#确定列表不是空的，列表是空的前一个if返回False，打印else中信息
titdds = []
if titdds:
    for titdd in titdds:
        print("adding" + titdd + ".")
    print("
hahaha")
else:
    print("didididi")

didididi

#使用多个列表
yuans = ['aa','bb','cc','ss']
adds = ['tt','aa','ll','pp']
for yuan in yuans:
    if yuan in adds:
        print("yeyeyey")
    else:
        print("nononon")

yeyeyey
nononon
nononon
nononon

#设置if语句的格式

== >= <=等比较运算符左右各一个空格

if age  < 4: